Uighur, also called "Huihe" or "Huihu", was one of the Tiele tribes in Outer Mongolia Plateau. It's the ancestor of Uyghur nationality in Xinjiang and The Yugu nationality in Gansu province. During the last period of Sui dynasty and the start of Tang dynasty, they once scattered in Outer Mongolia Plateau, and then established a subsidiary of Turkic khanate and the Xueyan Tuo khanate. Conformed to the trend of the times, Uighur chose to establish close relationship with Tang Dynasty, and with its help, Uighur finally unified other Tiele tribes and founded the Uighur Khanate in Mongolia. This paper concludes the 23-year's history of emperor Taizong period during which the Uighur Khanate was established.