Abstract: In order to explore the management measures to improve the biodiversity of mixed forest of Larix principis-rupprechtii, through investigations and monitoring of understory plant communities in mixed forests of Larix principis-rupprechtii subjected to four different thinning intensities-control group（Ⅰ）, light（Ⅱ）, moderate（Ⅲ） and heavy（Ⅳ）-within the Beijing Forest Farm, this study analyzed variations in understory vegetation. Results revealed that under the four thinning intensities, the number of understory shrub species were 5, 7, 7, 6 respectively, while herbaceous species were 11, 11, 10, 12, respectively. Shared species encompass species included Rubus crataegifolius, Corylus heterophylla, Spiraea salicifolia, Deutzia scabra, Deyeuxia pyramidalis, Carex tristachya Thunb., and Crepidiastrum lanceolatum. As the forest canopy closure decreased, the number of shrubs and herbaceous plants increased. In the moderate thinning intensity plots（Ⅲ）, the number of shrubs was the highest, while in the heavy thinning intensity plots（Ⅳ）, the number of herbaceous plants was the highest. Increased thinning intensity prompted a rise in light-loving shrubs such as Zabelia biflora, Sambucus williamsii, and Forsythia suspensa, underscoring the sunlight’s impact on vegetation. Significant variations were observed in the ranking of importance values of shrubs and herbs across different thinning intensities. Notably, species like Spiraea salicifoliaandRubus crataegifoliusconsistently ranked among the top three in all intensities. However,Corylus heterophyllaonly appeared in the top three at control group（Ⅰ）, whileForsythia suspensawas exclusive to heavy thinning（Ⅳ）. In the herbaceous layer,Deyeuxia pyramidalisranked among the top three in light and moderate intensities, with a particularly high value of 37.16 in the heavy intensity（Ⅳ）. Analysis of species diversity, community similarity, and understory diversity suggested that different thinning intensities influence species composition and diversity, increased thinning intensity positively impacted diversity, especially in the herbaceous layer. The results of this study provide an important reference for optimizing the management strategy of mixed larch forest ofLarix principis-rupprechtiito improve the conservation effect of biodiversity.