When the Anti-Japanese War broke out, Li Changnian moved west to Chengdu with Jinling University and continued his studies in the difficult environment of the war years. He completed college studies in 1938 and received a bachelor's degree in agriculture from Jinling University. After graduating from university, Li Changnian applied to be the chief editor of the monthly "Agricultural News" of the Central Agricultural Experimental Institute. This publication was the only national agricultural science and technology publication at that time. It was located in the Chongqing Office of the Central Agricultural Experimental Institute. Here, you can have priority in reading agricultural books and periodicals from all over the world, and have the opportunity to communicate with experts and celebrities in the domestic agricultural field, so that Li Changnian, who has just entered the society, has learned a lot of social practical knowledge that cannot be learned in books.
During this period, in addition to editing the "Agricultural News" magazine on a regular basis, Li Changnian also wrote "Production of Food and Clothing Raw Materials in the Southwest in the Past Three Years", "Achievements in Agricultural Science in the Past Three Years", "Enemy (Japanese) Country" "The Failure of Agricultural Policy" and other articles, and also translated and introduced various agricultural treatises from Britain, the United States, France, Germany, the Soviet Union and other countries. The China Agricultural Heritage Research Laboratory is a specialized research institution on agricultural history organized by the Ministry of Agriculture in 1955. Its predecessor can be traced back to the Agricultural History Research Laboratory of Jinling University Library in 1921. A national research unit with rich data accumulation and profound research foundation. Its main task is to summarize China's agricultural production experience over thousands of years and explore its development patterns, so as to provide historical reference for the country in formulating agricultural development plans. At the beginning of the establishment of the laboratory, the relevant departments at higher levels assigned the task of systematically exploring and sorting out China's agricultural production experience over thousands of years. After accepting this task, the Agricultural Heritage Research Laboratory concentrated the main scientific research strength of the laboratory and collected data from the vast historical materials. , carefully selected, carefully researched, eliminated the rough and retained the essence, and compiled a "Selected Collection of Chinese Agricultural Heritage". Li Changnian selected and compiled three albums from the series, including "Beans", "Hemp" and "Oil Crops". He also did review work for five other albums such as "Rice", "Wheat", "Cotton", "Miscellaneous Grain", and "Citrus". While working on the selection and compilation of the first volume of the large-scale agricultural history data series "Chinese Agricultural Heritage Anthology", Li Changnian also participated in another more ambitious project of collecting and organizing Chinese agricultural history data by the Agricultural Heritage Research Laboratory. Under the leadership of Wan Guoding, director of the research office at the time, together with all researchers in the office, they went to more than 40 large and medium-sized cities across the country and copied "Agricultural History Materials" from more than 4,000 ancient books in more than 100 libraries and some private studies. 613 volumes; in addition, 680 volumes of "Chinese Local Chronicles and Agricultural History Materials" were extracted from more than 8,000 existing local chronicles. This batch of materials is still collected in the form of manuscripts in the China Agricultural Heritage Research Laboratory, and is known as a unique large-scale unique copy of Chinese agricultural history materials. Over the years, many experts, scholars and graduate students at home and abroad have gone to the China Agricultural Heritage Research Laboratory to check out this batch of materials. They have used it to complete a large number of research projects and achieved a series of research results, which have greatly promoted the research on Chinese agricultural history and promoted research at home and abroad. Academic exchanges have played an important role.
Based on the collection of historical documents, Li Changnian participated in using modern academic theories and methods to conduct systematic and in-depth research on many issues in China's agricultural history. He was appointed as the editor-in-chief of the "Agricultural History Research Collection" and The editor-in-chief of "Selected Chinese Agricultural Heritage" and other special papers. Among these research albums, Li Changnian wrote papers such as "Soybean Cultivation and Utilization in the Motherland", "Ramie Cultivation Technology in the Motherland", "Timely Issues in Agricultural Production", and "Collation and Analysis of Farm Management Knowledge in the Motherland". In 1958, under the leadership of the new director Chen Hengli, the China Agricultural Heritage Research Office organized all the key researchers in the office to write a "History of Chinese Agricultural Sciences". Li Changnian served as the chief editor of the first volume of the book, and was specifically responsible for the research and writing of chapters such as "Investigation and Research on Agricultural Science by Yu, Gong, and Zhou Li in the Classics of Mountains and Seas" and "The Development of Qi Min Yao Shu on the Principles of Crop Cultivation". The first volume of the manuscript was submitted to Science Press for publication in September 1959. Then I started writing the next volume. The manuscript of the second volume was completed on the eve of 1966. It was not until 1984 that Li Changnian revised and finalized the manuscript and sent it to Science Press for reprinting and distribution together with the first volume. Although the first and second volumes of "History of Chinese Agricultural Sciences" were published nearly 20 years ago, the real academic achievements can withstand the baptism of the times and the test of history. As soon as the book came out, it received attention and praise from the academic community. Many well-known universities at home and abroad designated it as a teaching reference book for history graduate students. Many famous scholars quoted the historical materials and opinions in their monographs. In 1985, the Ministry of Agriculture, Animal Husbandry and Fisheries awarded the "History of Chinese Agricultural Science" the first prize for scientific and technological progress. Under the impact of the "Cultural Revolution", the China Agricultural Heritage Research Laboratory was revoked and disbanded in 1970. This distinctive national agricultural history research institution established in the early days of the founding of New China fell into disarray overnight. Like his colleagues, Li Changnian was sent to "farms" and "cadre schools" to participate in production labor. Soon he was assigned to a unit that had nothing to do with agricultural history research, and was engaged in work that had nothing to do with his academic expertise. He was simply sent home to live in peace and quiet.
Li Changnian later recalled: "At that time, I was in middle age. I was full of energy but did nothing. I wasted ten good years. What a sad thing for a scholar!" Fortunately, when Li Changnian was at home, , Shanghai Science and Technology Press, through the relevant departments of Jiangsu Province, invited him to write an "Agricultural History" suitable for general readers. He cherished this rare opportunity and used the most understandable language and the most detailed and concise information. The 10,000-year history of China's agricultural development is vividly, interestingly, and poetically picturesque. After the book was published in 1981, it was reprinted that year and reprinted many times thereafter. It once set a record for the most agricultural history book circulation, and reprints are also available in Taiwan Province of China.