Combined with the latest drilling, logging and seismic data we carry out numerical simulation to better understand the characteristics of the late Himalayan paleostress evolution in the Kuqa Depression, Tarim Basin. Using finite element numerical simulation method we obtained the three-dimensional distribution of the late Himalayan stress field in the Bashijiqike Formation in the Kelasu tectonic belt whereby accurately determined the paleostress state. By analyzing the relationship between the paleostress state and macrostructural style, fracture occurrence and reservoir physical properties, the geological and mechanical response to the paleostress state transition was systematically revealed. Finally, the influece mechanism between the paleostress state transition and reservoir physical properties was revealed by means of discrete element numerical simulation. During the late Himalayan, the stress field gradually transformed from a thrust-type stress field to a strike-slip type stress field at a depth range of 6500-7500 m. Above 6500 m depth, under thrust stress field, the compaction hole reduction increased with increasing burial depth, and the stress state and rock strength were not conducive to the development of fractures. Below 7500 m depth, the strike-slip stress field was conducive to the preservation of reservoir pores and rock fracturing. The above results deepen the understanding of the tectonic settings, reservoir properties and rock mechanical properties of the Kuqa Depression, suggesting the paleostress state transition provided the mechanical basis for the formation of large and medium-sized oil and gas field in the ultradeep reservoir of the Kelasu tectonic belt. This discovery has guiding significance for the next stage oil and gas exploration and development in the Kelasu tectonic belt.