The formation of Tibetan dialects is closely related to society,history,and natural environment. In the process of formation,the massive migration of Tibetans in Tubo Period which laid a foundation for the geographical distribution of Tibetan language was an indispensable prerequisite; the peculiar natural environment of the Qinghai-Tibet Plateau was a necessary condition; the varied speed of the development of Tibetan language in different areas due to different economic types was an important cause; the language contact caused by ethnic contacts was an important factor; and the administrative divisions in Tibetan areas in the Yuan Dynasty played an important role. Therefore,the formation of Tibetan dialects was a result of the gradual development of Tibetan language through the interaction of various factors such as society,history,and natural environment.