Abstract: In this paper, the relationship between the vegetation distribution and the environment of the middle stretch of Tianshan M. was quantitatively investigated with the methods of DCA ordination, Twinspan classification and CCA analysis. The spatial distribution of plant communities in this area has one center and two extreme points, that is, from one center (kinds of moist plant communities inside Tianshan M. )to the dry and cold extreme points of the northern slope and dry and hot extreme points of the southern slope. Further study found that types and patterns of plant communities in the studied region were determined on large scale by precipitation and temperature. On the middle and small scales the type and pattern were determined by soil humidity and soil nutrient. This conclusion explained why there were different plant community types where landforms were similar in inside Tianshan M. The spatial distribution of plant communities, the key environmental factors and environmental interpretation by mathematical models were presented in this paper.