The observation during the reign of Emperor You of Song Dynasty recorded the human habitation and degeneracy of 345 stars, which was the catalog with the largest number of stars before the introduction of western catalogs in the early Qing Dynasty. In the Song Dynasty, Yao Shunfu made an observation during the years of Chongning in order to compile the Calendar of the Ages. The observation accuracy was very high, the measurement error was only .15 degrees, and the distance between 28 nights was updated again. In Yuan Dynasty, Guo Shoujing was good at both instrument manufacturing and astrometry. Compared with Yao Shunfu, his observation accuracy was improved by one step: the average measurement error of the distance of 28 nights was less than .1 degrees.