Abstract: Due to factors such as groundwater and hydraulic permeability improvement technology，coal seams have different water content in the coal body. Coal seams with different water content have a great influence on their mechanical properties and gas flow in the coal seam，thus causing difficulties in gas extraction.In order to solve the difficult problem of water-bearing gas extraction，this paper adopted the Guhanshan bituminous coal and Zhaogu anthracite to conduct the acoustic wave test of coal samples with different water-bearing saturation in the experiment，and analyzed and studied the law by combining the Gassmann equation assumed by Wood theory and the kuster-toksoz theoretical equation.It is found that the water saturation of both ancient hanshan bituminous coal and zhaogu anthracite is 60%. The parallel bedding water saturation before 60% conforms to Gassmann equation assumed by Wood theory，and after 60% conforms to kuster-toksoz theoretical equation. However，vertical stratification pores and fractures are relatively developed，and the water saturation before 60% is inconsistent with Gassmann equation assumed by Wood theory. Therefore，the author established a modified formula to calculate wave velocities of different water saturation，which is basically consistent with the actual wave velocities. After 60%，it conforms to the kuster-toksoz theoretical equation. It provides a theoretical basis for defining the wave velocity variation rule of coal body under different water saturation.