Abstract: In order to obtain the influence law of moisture on mechanical properties of coal, and provide the basis for the research of coal seam affusion to prevent and control percussive ground pressure and coal and gas outburst, the paper simulates the influence of moisture on modulus of elasticity and compression strength of coal. The paper uses the method of numerical simulation to simulate the change of elastic modulus of different moisture of coal after coal seam affusion; experimental simulates the change of compression strength of coal with different moisture and confining pressure. The results show that the elastic modulus becomes low around the injection hole after the coal seam affusion, from 740 MPa to 540 MPa, which makes the elastic modulus down to about 60% of the original coal body. As the increase of moisture,the compressive strength of the coal has been declined, the relational expression of compressive strength and moisture is R=5.053 8e^{-0.169 7W},and determines that the reasonable injection of coal seam affusion is 6%-8%.