This study used historical linguistics and phonology method for cross analysis medieval and contemporary Turkic, Uighur, Mongolian, Manchurian and Turkish on the origin and meaning of the title of "Mou-yuan" Khan, also by ways of documentary archives, inscription and the masterpieces written by historians of Sinology. The author verify that "Mou-yuan" Khan has no doubt to do with the Turkic vocabulary "Bay" (abundance, wealth) directly for sure.
