Insect diversity is widely used in ecological restoration evaluation. In order to understand the effects of different ecological improvement measures on insect diversity in the south mountain of Lhasa, the insect diversity under four typical tree species assemblages were investigated from May to September 2023 by using the Malaise traps and the sweeping net. Results : 1) A total of 29576 insects were collected in this survey, belonging to 13 orders 120 families and 246 species, including 112 unknown species. The dominant families were Chironomidae and Chloropidae, accounting for 16.71 % and 11.89 %, respectively. The dominant species was the Trachysiphonella ruficeps, accounting for 11.6 %. 2) The individual number, group number, Shannon-Wiener index, richness index and evenness index of insect in Hippophae rhamnoides + Pinus tabuliformis + Robinia pseudoacacia + Juniperus przewalskii + Populus beijingensis（S1）were the highest, which were significantly different from those in Hippophae rhamnoides + Pinus tabuliformis + Salix microstachya + Picea asperata（S2）and Hippophae gyantsensis + Pinus tabuliformis + Salix microstachya + Pinus bungeana（S3）（P<0.05）. Hippophae gyantsensis + Pinus tabuliformis + Picea asperata + Pinus sylvestris（S4）had the highest insect dominance, which was significantly different from the other three tree species assemblages（P<0.05）. 3) The number of individuals and groups of insects in the four tree species assemblages peaked in July and August, showing a single-peak trend, which was significantly affected by time. The individual number of insects in S4 fluctuated greatly. 4) Non-metric multidimensional scale analysis ( NMDS ) showed that the composition of insect communities in different tree species assemblages did not overlap. Further similarity analysis ( ANOSIM ) showed that the difference between groups was significant ( R = 0.963, P = 0.001 ). Combined with Jacard and S?rensen index, it showed that the composition of insect community in S4 had the lowest similarity with the other three tree species assemblages. 5) Redundancy analysis（RDA）results showed that the index of herb evenness and richness significantly affected the number of insect groups and individuals ( P < 0.05 ). The ecological forest of Lhasa south mountain was in the early stage of establishment, and did not form a stable insect ecosystem. The insect community had poor ability to resist the outside world. The insect community of S1 was relatively stable and S4 was the lowest in the four different tree species assemblages. At the same time, the influence of understory herbs on the stability of insect community in ecological forest can not be ignored.