Miaoxi Sag is located in the southeast of Bohai Bay, and it is made up by the North subsag, the East subsag and the South subsag. The seismic interpretation and fracture analysis show that the North subsag and East subsag is respectively constituted by two dustpan-shaped fault depression, it is graben structure in the north of South subsag, and dustpan-shaped fault depression in the south. The influences of Tan-Lu fault zone on each subsag are different. The North subsag and East subsag are influenced by extended tectonic system, and the South subsag is influenced by Tan-Lu fault. The extended faults in the three subsags are caused by the strike-slip faults, constituting a part of strike-slip tectonic system, and the shallow faults are transformed by Zhangjiakou-Penglai fault zone.