Abstract: In recent years, the exploration investment in the eastern South China Sea continues to increase, and higher requirements have been placed on the efficiency of field operations in well site surveys. Based on the available well site investigation information in nearby regions, this method optimized the design plan of the semi-submersible well site investigation in mature exploration area where the probability of shallow layer geological hazards is low by using methods such as reducing the density of simulative geophysical survey line and the amount of the soil sample in seabed. And, the method focuses on surveying the area near the well center. The application results show that this method can still provide reliable geological information for the safe operation of the semi-submersible drilling platform when the data area of the well site is reduced, and greatly improve the efficiency of well site investigation work.