Bohai Sea was traversed by the Tanlu fault belt, and the formation of faults in Bohai Sea is relative to the strike-slip of Tanlu fault belt. The dextral slip of Tanlu fault and the conjugated sinistral slip of the Zhangjiakou-Penglai fault have occurred since the Eogene period. The two faults respectively controlled the formation of small faults in Laizhou Bay to Middle Bohai Sea to Liaodong Bay areas and the western Bohai Sea. The small faults mainly distributed along the strike slip faults and had the strikes of NE, NEE, EW and NWW directions, among them, the NE and NEE directions are the main strikes.