Abstract: Ultra-high pressure generally occurs in the Middle Permian Lucaogou formation of Jimusar sag, Junggar basin. This paper analyzes the present formation pressure features and the ultra-high pressure formation mechanism and reconstructs the paleopressure evolution of Lucaogou formation by using logging, drilling, formation testing data combined with basin modeling technology. The study results show that the present pressure structure can be categorized into four zones from top to bottom such as normal pressure zone, shallow ultra-high pressure zone, transitional zone and deep ultra-high pressure zone. Lucaogou formation is located in the deep ultra-high pressure zone which is continuous laterally. Most residual pressures range from 10 to 20 MPa and the pressure coefficient is 1.10~1.50. The paleopressure evolution of Lucaogou formation experiences three and a half cycles of pressurization—decompression and there is a good matching relationship among the pressure cycle, sedimentation rate, hydrocarbon generation and expulsion and tectonic uplifting. Undercompaction resulted from the rapid burial of sediments is the main reason causing the first stage of ultra-high pressure. After reaching the hydrocarbon generation threshold in Late Triassic, hydrocarbon-generating pressurization was the key mechanism for the second and third stages of ultra-high pressure