Abstract: The Laixi fault was identified and described, and its geometric features and formation mechanism were also analyzed based on the gravity data and new 2D seismic data of the Laiyang Sag in order to clarify the fracture properties and formation mechanism of the Laixi fault. Several structural styles were found in the Laixi fault, such as zonal distribution, flower structure and dolphin effect. The geologic bodies on both sides of the fault showed a sinistral offset of 4.4 km, indicating a typical sinistral strike-slip fault. From the Late Cretaceous to Paleocene, the tectonic stress field in the study area was NEE-SWW compression. The activity of the Muping-Jimo fault zone converted from extension to dextral strike-slip, while the Laixi fault had an opposite direction, which was a conjugate strike slip fault of the Muping-Jimo fault zone. The Laixi fault did not control the sediment of the Cretaceous; therefore, it was not a concave boundary fault in the west of the Laiyang Sag, but an internal split fault, which cut the Laiyang Sag into two parts.