Abstract: Using the method of 1 km × 2 km mechanical distribution, a total of 74 sample plots with the species composition ≥ 60% were investigated in northern Anning River basin, in Dechang County, Sichuan Province, to explore the diversity of stand diameter of Pinus yunnanensis community. The results showed that there were 2 758 trees with DBH ≥ 5 cm were investigated in 74 sample plots, with an average density of 932 plants·hm⁻². The diameter class was mainly 6-20 cm, accounting for 84.63% of the total number of plants. The Shannon Weiner index and Simpson index of Pinus yunnanensis diameter order fluctuated greatly compared with the whole population. The canonical correspondence analysis showed that the distribution and diversity of diameters were mainly affected by density, altitude and slope. In summary, the diversity of diameter of Pinus yunnanensis community was affected by the changes of density, elevation and slope.