Abstract: In order to explore the altitude distribution of plant species composition and diversity in Baima Snow Mountain Nature Reserve, the plants in 7 plots along the elevation gradient (2300-3500m) were investigated. The results showed that: 1) There were 145 species of vascular plants belonging to 52 families and 87 genera in Baima Snow Mountain Nature Reserve were recorded in 7 plots investigated. 2) The richness index and Shannon-Wiener index of tree layer first increased, then decreased and then increased with the elevation, while the richness index and Shannon-Wiener index of shrub layer first decreased and then increased with the elevation. The two indexes of herb layer showed a downward trend. The Simpson index and Pielou index of tree layer, shrub layer and herb layer all decreased at first and then increased with the elevation. 3) The Cody index of tree layer, shrub layer and herb layer increased at first and then decreased with elevation. In conclusion, the composition of plant species in Baima Snow Mountain Nature Reserve was complex. The plants of different life forms showed different diversity distribution pattern along the altitude gradients, while the different sensitivities of different plant species to environmental heterogeneity and climate may be important factors affecting the diversity distribution pattern of plant species diversity.