Abstract: Blue sheep (Pseudois nayaur) are widely distributed in Qinghai-Tibetan Plateau and its surrounding areas. Wanglang National Nature Reserve is located in the eastern margin of Qinghai-Tibetan Plateau, but there are few studies on the population quantity and distribution of blue sheep in this reserve. From May 2020 to August 2021, the number and distribution of blue sheep in Wanglang National Nature Reserve were investigated by using the line transect method. A total of 1 012 blue sheep were recorded, among which 117 were single sheep and another 895 were integrated into 142 groups, with a mean group size of 6.31±1.52 (2~36). Small group size with 2 blue sheep was the most common group size, accounting for 11.86% of the total population. Among the 142 groups, mixed groups were the most frequently observed, accounting for 65.49% of the total number of group. The result of Distance 6.0 showed that the number of blue sheep in Wanglang National Nature Reserve was about 3 144 (1 989~4 970). In Wanglang areas, blue sheep were distributed in five areas: the first branch ditch of Dawodang, the first branch ditch of Zhugencha, the second branch ditch of Zhugencha, the Tiebanfang, and the Great Lawn. The altitude distribution range was 2 000~3 679 m, and the main altitude distribution was above 3 000 m. The results of MaxEnt model showed the grazing, vegetation type, altitude and distance from settlement were the main environmental factors related to the distribution of blue sheep in this reserve. The MaxEnt model and ArcMap calculation results showed that there were 181.25 km² suitable habitat area, 56.42 km² sub-suitable habitat area, and the total area of the two parts was 237.67 km², accounting for 73.59% of the nature reserve. This study enriched the basic data of the distribution characteristics and quantitative estimation of blue sheep population in Wanglang National Nature Reserve, and put forward some target suggestions for the management of the reserve, which is of great significance for the protection of blue sheep and their habitats.