Precipitation is the most important factor restricting the structure and species diversity of plant communities in arid and semiarid areas. In recent years, the variation patterns of community species diversity along environmental gradients have become one of the research hotspots in ecology. However, many controversies about the response of plant community characteristics to changes in natural precipitation remain unresolved. In the arid area of Qinghai province, one of the dominant tree species is Juniperus przewalskii, which plays a key role in water and soil conservation, water holding, and ecological balance. Studying the changes in age structure, community composition, and species diversity of J. przewalskii population along the annual precipitation gradient is important for the conservation of natural plant communities in arid areas. This study was conducted to understand the response of the community characteristics of J. przewalskii and the age structure of its population to annual precipitation gradient. The natural community of J. przewalskii in Qinghai province was taken as the research object, and a community sample plot was laid out along the annual precipitation gradient. The community characteristics of this species were also investigated. Results showed that (1) annual precipitation increased gradually from northwest to southeast in this area. As annual precipitation increased, the importance of dominant species in the shrub and herb layers of J. przewalskii communities changed significantly (P<0.05). (2) When the annual precipitation was between 169 and 377 mm, the population decreased. Conversely, the population remained stable at annual precipitation of 470 mm, but it increased at annual precipitation of 530 mm. (3) The α diversity index of understory plants was significantly different under various annual precipitation levels (P<0.05). As annual precipitation increased, the Shannon-Wiener index, Simpson index, and species richness of shrub and herb layers increased gradually and reached the maximum values when the annual precipitation was 530 mm. (4) As annual precipitation increased, the β diversity index of the shrub layer fluctuated. Cody and Sorensen indices peaked and reached a trough value when the annual precipitation levels were 470-530 and 281-377 mm, respectively. The β diversity index of the herb layer increased first and then decreased. The Cody and Sorensen indices peaked and reached the trough value when the annual precipitation ranged from 377 mm to 470 mm. The maximum β diversity and the fastest rate of species replacement were observed in this gradient. Annual precipitation significantly affected the age structure and community characteristics of J. przewalskii population. In a forest area with annual precipitation of less than 377 mm, the following measures should be implemented to promote the health and stability of communities: the microtopography of the forest should be transformed, surface roughness should be increased, natural precipitation should be collected, and management and protection should be strengthened to prevent injury to cattle and sheep and thus facilitate natural regeneration.