Abstract: The western part of South China Sea is one of China's shale oil resource-rich areas. Limited by its marine environment and harsh operating conditions, traditional shale oil development technologies are difficult to apply. Therefore, it is urgent to explore technologies suitable for offshore shale oil development. In this paper, the seawater-based fracturing fluid with high temperature and high salinity resistance is optimized through laboratory experiments. Firstly, its swelling, crosslinking, pickup, anti-swelling, static filtration and reservoir protection performance tests are carried out. Secondly, according to the formation characteristics, the proppant is optimized, the tubing string structure is optimized and the critical erosion rate is verified. Finally, the field fracturing test is carried out by using the real-time data transmission system combined with reasonable equipment placement. The results show that the optimized wellhead tubing string meets the main fracturing 6 m³/min displacement construction. The resistance reduction rate of seawater-based fracturing fluid construction is 65%. The actual fracture parameters after fracturing are better than the designed parameters. The seawater-based online fracturing technology has achieved good stimulation effect, which provides a feasible technical route for the development of offshore shale oil resources.