Abstract: Based on a synthetic analysis of regional geological data available in western yunnan and a correlation of these data with the geological conditions of Southeast Asia, this paper discusses the mechanism for formation of stanniferous granite of western Yunnan due to plate motion and the grounds for its division into belts. The belt between the Lancang River of western Yunnan and the Naga Mountains of Burma may be called the Yunnan-Burma landmass, which originally belonged to the margin of Gandwanaland before disintegration. In its eastern part a late Proterozoic-early Mesozoic trench-arc-basin system developed under the attion of the Lancangjiang subduction zone. Stranniferous granite of the eastern belt （the Yunlong-Menghai granite belt） and that of the western belt （the Changning-Ximeng granite belt） initiated in the process of development and evolution of this mobile plate margin belt). Granite in the Tengchong-Lianghe area represents a back-arc granite belt formed after cessassion of subduction of the Lancangjiang subduction zone under the effects of the subduction of the forefand oceanic crust of the Indian plate in the western part; thus it is correspondingly called stanniferous granite of the western belt. The stanniferous granites in the three belts of western Yunnan are characterized by different genetic mechanisms, petrological features and mineralization, but their main characteristics are similar to those of corresponding belts in Southeast Asia in many respects. By a serious comparison, the authors hold that the whole stanniferous granite belt of western Yunnan is precisely the northward extension of the stanniferous granite belt of Southeast Asia.