Abstract: The complex terrain and hydrodynamic environment in the South China Sea bring challenges to scientific observation. Combining the advantages of various observation platforms to form an ocean observation network is the future direction of observation in the South China Sea. In this paper, mooring array and underwater glider as the main fixed-point and mobile observation means, are selected to design the positioning strategy in the middle of the South China Sea. The data assimilation system is constructed based on the regional ocean model system, and the observing system simulation experiments is designed. Then, by comparing the assimilation results of temperature and salinity observation data of mooring array and underwater gliders with different schemes, the observation strategy of their combination is discussed. Between 0 and 1 000 m water depth, the simulation experiments results show that limited by the number and distribution of stations, when only the mooring array data is assimilated, the improvement of temperature and salinity assimilation accuracy is finite; The addition of underwater gliders observation data makes the improvement more obvious. The improvement of temperature assimilation is mainly reflected in 100-500 m, and the improvement of salinity assimilation is mainly reflected in 100-250 m, which corresponds to the peak depth range of the root mean square error in initial temperature and salinity assimilation results respectively; The initial positioning and the movement mode of the underwater gliders also have an impact on the experimental results. For the central South China Sea, the horizontal rightward movement sampling of the underwater gliders is slightly better for temperature assimilation, and the cyclic sampling near the initial position is better for the assimilation of salinity and sea level anomaly. The simulation results of the observing system simulation experiments can provide reference for the future design of ocean observation networks in the South China Sea.