Abstract: The acoustic parameters of the seabed in the northern South China Sea were inversed using the experiment data from an acoustic experiment in 2015. Based on the comprehensive analysis of the influence of the sound speed fluctuation and the submarine model on seabed inversion, the multi-parameter hybrid acoustic inversion scheme is improved by selecting the equivalent sound speed profile and the submarine model to apply in the thermocline environment with fluctuation. In other words, mean sound speed profile and half infinite bottom model are used in forward sound field calculation to save the inversion dimensions. The inverted seafloor velocity and density are in good agreement with the core sampling measurements. The nonlinear empirical relationship of the attenuation coefficient with frequency is given out. The inversion results are meaningful to the sound propagation research and application in the northern area of the South China Sea.