Offshore wind energy resources is richer than land wind energy, and water depth of the continental shelf in China's waters increases slowly as the distance offshore increases. Based on the characteristics, how to optimize the design of mooring systems to adapt to the water depth conditions in China is one of the major problems encountered in the development of floating wind turbines. In this paper, a 5MW-OC4 semi-submersible floating wind turbine was used as the research object, the floating wind turbine was moored by suspended chain lines, and the frequency domain and time domain calculations of the floating wind turbine were performed under 40 m water depth in a sea area of Bohai Sea using SESAM software. Mooring accessories were used separately and in combination for parameter sensitivity analysis, and then the mooring system was optimized by combining buoys and clump weight blocks. The results of the study show that under shallow water conditions, the combination of mooring fittings has the same effect on the overall response of the floating wind turbine as changing the same mooring parameters when used alone, but the effect of changing the mooring parameters on the optimisation of the performance of the mooring system is more obvious when used in combination, the optimisation difference in the mean value of the counterweight block position parameters when used in combination can reach 15.7%, and the optimisation difference in the longitudinal oscillation, longitudinal rocking and the tension response are all within 10% of each other. The optimisation difference of longitudinal oscillation, longitudinal rocking and tension response is basically within 10%. Therefore, choosing a reasonable combination of accessories can significantly change the overall characteristics of the floating system and affect the safety and cost of the system.