Abstract: Since the Yuan Dynasty, Yongning Prefecture and Yanjingwei, like other regions in the southwest, have been ruled by Moso chieftains in different places. Since the Ming Dynasty (1368-1644), with the expansion of the Mu chieftain's power of Lijiang, they entered this area and gradually occupied most of Yongning Prefecture and Yanjingwei, which triggered years of wars and disputes. Since 1436, the Ming Dynasty conducted several mediations between the conflicting sides, but did not punish the military actions of Chieftain Mu. The reason was that generations of Mu chieftains gained trust and support of the Ming Dynasty through decades of "serving the country in good faith", so that the Mu chieftains in the Ming Dynasty had great independent political rights and applied them to the maintenance of social order. From the perspective of the Ming Dynasty, in the regions ruled by chieftains, only with the support of the central court could they exercise the power of chieftains and, through this chieftain system, the local and the central court could be organically linked. The local chieftains also used this system to expand their power to the surrounding areas.

Key words: Moso, the Mu Chieftains, Yongning Prefecture, Yanjingwei, tusi (chieftain) system