According to the theory of hydrocarbon downward migration, based on seismology, geochemistry, well drilling and logging, it is discussed in this paper the accumulation mechanism of petroleum downward migration in the western Chezhen Sag, the Jiyang Depression, the Bohai Bay Basin. The main pathways of hydrocarbon downward migration include factures or micro cracks in the process of secondary migration, and the formation process of hydrocarbon downward migration is reproduced by experimental simulation. Source rocks in the middle and lower subsections of the 3rd member of the Shahejie Formation have good genetic relationships with oil sands from the upper subsection of the 4th member of the Shahejie Formation, and reservoirs discovered in the upper subsection of the 4th member of the Shahejie Formation are buried deeper than the bottom boundary of source rocks from the 3rd member of the Shahejie Formation. In the lower subsection of the 3rd member of the Shahejie Formation, pressure coefficients range from 1. 0 to 1. 4, and decrease both upwards and downwards, providing force for petroleum downward migration. Cracks and fractures break the mudstone interlayers between the bottom boundary of source rocks from the 3rd member of the Shahejie Formation and the top surface of the 4th member of the Shahejie Formation. As a result, source rocks and reservoirs are connected.% 以油气倒灌理论为指导，综合利用地震、地化、钻井、测井等资料，研究了渤海湾盆地济阳坳陷车镇凹陷西部油气倒灌的成藏机理.通过实验模拟油气在二次运移过程中以断裂(或微裂缝)为倒灌通道的过程，再现油气倒灌的形成过程.研究表明， Es3(中-下)亚段烃源岩与 Es4(上)亚段油砂具有较好的亲缘关系，且 Es4(上)亚段发现的油藏埋深大于 Es3烃源岩底界埋藏深度；Es3(下)地层压力系数在1.0~1.4之间，向上和向下压力系数均逐渐减小，是油气倒灌的动力；裂缝与断裂是切穿 Es3烃源岩底界与 Es4顶部之间泥岩隔层、连接烃源岩与储集层的运移通道.
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