Abstract: Water content has an important influence on acoustic wave velocity of coal and rock body, and pore structure and the cements contained directly affects water content of coal and rock body.Thus, the pore structure, the cements contained and absorbing capacity of coal and rock body are analyzed by scanning electron microscopy (SEM).Then the acoustic wave velocities of coal samples under different water absorption conditions are measured by absorbing water at normal temperature and pressure, and the variation law of wave velocities of coal and rock body with different water content is explored.The research results show that a small amount of micro-pore and cementitious debris exist on the surface of Guandi coal sample.On the surface of Malan 8# coal samples are no obvious pore and fissure structure exist, but more cementitious debris can be seen.The water absorption of coal and rock body in Malan 8# coal samples is 2.49%, while that of coal samples in Guandi coal sample is only 1.31%.With the increase of water absorption, the velocity of longitudinal and shear waves in coal and rock body tends to increase.The mechanism of wave velocity variation is mainly influenced by the water content and the elastic modulus of coal and rock body.