Abstract: According to the influence of the water pressure on the coal permeability, it used relative permeability coefficient as the main reference quantity, then it used the experimental method to study permeability coefficient of the coal and the relationship between axial stress and water pressure H under different water pressures. The experimental results showed that in the low-pressure water injection process of hydrostatic pressure, the permeability coefficients of various coal samples were smaller and coal seam water injection H pressure had a significant impact on coal water injection permeability ; In the continuous loading process of the water injection pressure H from the low to the high pressure, the permeability coefficients of coal samples presented increasing trend, the axial pressure of coal samples decreased, and there was a critical injection pressure H_c; When the coal destruction happened, the critical water pressure H_c was greater than the axial confining pressure, tensile failure of the specimen came out, and the phenomenon of crack propagation conduction draining occurred; Index function and polynomial function , taking water pressure H as the basic variable, had better fitting to the changes of permeability coefficient and axial stress.