Abstract: According to the relationships among mechanics balance equation,the law of conservation of mass,permeability of coal seam,porosity,volume strain of coal,the gas-solid coupled equation of hydraulic flushing borehole in the coal seam floor is established.By simulating the changes of effective influence radius of hydraulic flushing borehole at different coal output,it obtains that the effective influence radius of hydraulic flushing borehole is increasing as the amount increasing of overflow coal and prolonging of drainage time.When the amount of overflow coal is 1 t/m,effective influence radius is 5.8 m,the effects of pressure relief and antireflection are very good.