To clarify the formation mechanism and evolution characteristics of the deep Permian overpressure in western Well Pen-1 Sag and its periphery in Junggar Basin， based on the data of drilling， logging， and measured formation pressure， the formation mechanism and evolution characteristics of overpressure were comprehensively studied， and the contribution rate of different types of overpressure genesis in the target layer was quantitatively characterized by using the methods of analysis of well logging curve combination， cross plots， and basin simulation. The results show that ① the overpressure genesises of different lithologies of the deep Permian in the study area have obvious differences， among which the overpressure genesises of source rock of Fengcheng Formation and the Lower Wuerhe Formation are mainly hydrocarbon generation and disequilibrium compaction， with hydrocarbon generation dominating； the overpressure genesis of mudstone caprock is mainly disequilibrium compaction， while the overpressure genesises of reservoirs of the Fengcheng Formation and Lower Wuerhe Formation are mainly overpressure transfer and disequilibrium compaction. ②The overpressure induced by hydrocarbon generation of Fengcheng Formation in the study area has appeared since the Early Permian and reached the maximum at present， and there are little differences in the size of the pressurization among different tectonic positions； the overpressure of the source rock is mainly distributed in the range of 39.43-49.16 MPa， but its contribution rate has obvious differences， with larger salients and smaller sags， and the contribution rates of pressurization induced by hydrocarbon generation in salients and sags to the total overpressure are 84.49%-94.41% and 65%-67.3%， respectively. The pressurization induced by hydrocarbon generation in the source rock of the Lower Wuerhe Formation has a similar size to that of Fengcheng Formation. The contribution rate of disequilibrium compaction to the overpressure in the mudstone caprock is basically 100%. ③ Overpressure transfer pressurizations in the Permian reservoir of the study area are mainly formed from the Late Jurassic to Early Cretaceous and since the Paleoproterozoic to now， and their contribution rates vary significantly in different salient areas， with 21.86%-23.35% and 100% in Dabasong Salient and Shixi Salient， respectively. Clarifying the overpressure distribution law of deep and ultra-deep formations in the study area can provide a basis for the further development of the new basin.