It is a phonetic symbol commonly used by China people and Mongolian ancients. It is formed on the basis of Uyghur alphabet. According to Chinese and foreign historical records, after Genghis Khan conquered Naiman in 1204, Mongols began to spell their own language with Uighur letters. This writing system is the predecessor of the present Mongolian language, and now it is called Uighur Mongolian language. Its letter pronunciation, spelling rules and lines are similar to Uyghur. Up to now, the letters of Uygur and Mongolian have not been recorded directly. According to the analysis of this written material by later generations, 19 letters were summarized. Five of them are vowels and 14 is a consonant. According to the different position of each letter in the word, the writing method changes slightly, and there are three variants of word segmentation: beginning, middle and end. Spelling is usually based on words, connecting books up and down. However, sometimes a word can be written in two paragraphs. The spelling rules are not strict, and repeated words are more common. Word order is from top to bottom, and line order is from left to right. There are three kinds of punctuation marks: single dot (equivalent to comma), double dot (equivalent to period) and four dot (used at the end of a paragraph). Ye Songgebei (1225) is the earliest existing Uighur Mongolian literature. After Kublai Khan of Yuan Shizu promulgated Mongolian New Characters (later renamed Mongolian Characters, now commonly known as Basiba) in 1269, the use of Uighur Mongolian was once restricted. At the end of Yuan Dynasty, Uighur Mongolian gradually became popular.