Yanchang Oildom has undergone two uplift-erosion

one hiatus and three subsidence processes since Late Tri-assic. The first subsedence stage(225～208 Ma)were mainly tectonic subsidence under comression; the second and the third subsedence stages(203～157 Ma and 138～97 Ma respectively) were mainly sedimentary loading subsidence in-tension environment. Simulation results show that the physicd property of Middle-Lower Jurassic Yanchang Formation resenoir is much better than that of the underlying Upper Triassic Yanchang Formation. Burial compaction was the primary cause resulting in 1500 porosity decrease of the sandstone of Jurassic sandstone and 200o that of of Triassic sandstone Mechamical compaction of overlying sedimentary loading formed in the second and the third subsidences resulted in worse physical property of the reservoir in the west part than that in the east part of the study area. It is suggested that the 4 +5 members of the Yanchang Formation have favourable trap function and could be regional caprock of Chang-6 member