Pinus densata Alliance is one of the most widespread pine forests in mountains of southwest China. Endemic to China, this alliance occurs in west Sichuan, northwest Yunnan, and southeast Xizang. In this study, we defined the geographic distribution boundary and priliminarily ascertained the geographic distribution area of P. densata Alliance based on previous literature and field investigation sites. Using data from 48 plots surveyed during 2020-2022, we proposed a preliminary scheme of vegetation classification and described the community structure characteristics for P. densata Alliance, and analyzed species composition characteristics combined with data from 11 plots surveyed in 2012. The results showed that (1) the distribution area of P. densata Alliance covered 33 counties and cities, including Yajiang, Xiangcheng, Daocheng, Dêqên, Xamgyi’nyilha, Markam, Mainling, and so on, at an altitude ranging from (1 300) 2 500 to 3 800 (4 000) m, and the eastern, western, northern and southern boundaries were Donggu Town in Danba County, Zengqi Township in Sangri County, Puxi Township in Zamtang County, and Yulong Snow Mountain in Yulong Naxi Autonomous County. (2) 522 vascular plant species belonging to 222 genera and 67 families were recorded, among which there were 500 seed plants belonging to 209 genera and 60 families, and 233 Chinese endemic plants belonging to 114 genera and 42 families, and the north temperate element was the dominant areal-type. (3) Based on the differences in community structure and species composition, P. densata Alliance could be classified into 7 association groups and 20 associations.