Based on 545reservoir pressure measurements in 186boreholes and the calculated shale pressure of 65boreholes using equivalent depth method, the evolution and distribution characteristics of overpressure in Damintun depression were studied by using numerical simulation method. The dynamic mechanism of hydrocarbon expulsion from the thick source rock was discussed through the integrated analysis of the evolution, distribution and activity of faulting in the depression. The results show that overpressure is extensively developed in the depression. Compaction disequilibrium resulted from high sedimentary rate and hydrocarbon generation are the main controlling factors for the development and evolution of overpressure. The numerical simulation shows that overpressure increased gradually from the period of Es_4and reached maximum at the period of Es₁. The development of overpressure is relatively slower in the faulting zone. It is suggested that overpressured fluid is mainly episodically expulsed from geopressured sediments. The dynamic mechanism of overpressure-dominated and tectonic-overpressure controlled episodic petroleum accumulation includes natural hydraulic fracture, mud diapir, faulting dominated and overpressure promoted.