Changchang Sag, located in the east of the deep water area of Qiongdongnan Basin, is an important potential area for oil and gas exploration. Based on high-precision three-dimensional seismic data, fine interpretation of complex faults in central Changchang Sag is carried out. According to the development position, combination form and structural style of faults, combined with the characteristics of regional stress, it is considered that there are two NWW trending extension-strike-slip composite faults in the study area, whose evolution can be divided into three stages: (1) in the Early Oligocene, under the action of NW-SE regional tensile stress, the main extension faults are developed; (2) in the early period of Late Oligocene, under the sea floor expansion of southwest sub-basin of South China Sea, the regional tensile stress rotates clockwise, and changes from NW-SE to SN, which produces dextral strike slip, resulting in a series of secondary faults; (3) from the late period of Late Oligocene to Early Miocene, the basement faults in Changchang Sag are continuously active, and the strike slip becomes more intense, resulting in the development of a large number of negative flower structure due to the enhanced obstructing of two rigid uplifts in the north and south of the depression. The north fault belt is characterized by right-slip faults with left step, which has good sealing due to the extrusion stress. The south fault belt is characterized by right-slip faults with right step, which is conducive to the hydrocarbon migration due to the tensile stress.