Lithologic reservoir developed well in Mesozoic Yanchang Formation of hydrocarbon accumulation area of Zhenjing area. In order to reveal the characteristics of low permeability reservoir formation and laws of hydrocarbon migration and accumulation in Zhenjing area，Chang7 and Chang8 members in Zhenjing area were selected as study targets to analyze the characteristics of clay compaction and fluid overpressure distribution in the Yanchang Formation. The results showed that the fluid overpressure of Chang7 member ranges from 8 MPa to 13 MPa，and the fluid overpressure of Chang8 member is lower and can reach to 10 MPa only in several areas. There are obvious differences in fluid overpressure between Chang7 and Chang8 members. The high overpressure difference offers the driving forces for oil and gas migrating from Chang7 member to Chang8 member. High oil production zones are areas where high overpressure difference exists between the two members and areas with relatively low overpressure difference are favorable for hydrocarbon migration and accumulation.The northeast and the southeast regions of the study area, which respectively have high overpressure difference and largescale low overpressure difference, are expected to be oil and gas enrichment zones.