Abstract:The temperature and pressure field is the key point for studying on the mechanism of hydrocarbon accumulation in the petroliferous basin, and the reconstruction of paleo-pressure particularly plays an important role in the study of hydrocarbon migration and accumulation, and even diagenesis in reservoirs and hydrocarbon generation for source rocks. In this paper, with pressure distribution as constraint, the paleo-pressures in the middle Permian of the northwestern Sichuan Basin were reconstructed by adopting basin modeling. In the northwest fault-fold belt of the Sichuan Basin two stages of overpressure developed, in the middle Permian, especially from the late Jurassic to the end of early Cretaceous.The overpressure accumulated rapidly in reservoirs under the effect of compressive stress which varied greatly in different structural units. The weak overpressure developed near the orogenic belt, which recovered to normal pressure after the late Cretaceous; but the strong overpressure developed in the fold and foredeep zone far from the orogenic belt even after the structure uplift, which was mainly controlled by the external compressive stress from northwest.