The invention provides a hole flushing device for coal mine downhole gas extraction drill holes. The hole flushing device comprises a water tank, a high-pressure pump, a high-pressure hard pipe, a high-pressure hose, a self-propelled drill bit, a base, a winch, a pushing mechanism and the like. The winch and the pushing mechanism are fixed to the base. The device can correspond to the drill holes in different positions and at different angles by adjusting all parts of the base. The high-pressure hard pipe can penetrate through the pushing mechanism before being fed into the drill holes. The high-pressure hard pipe can be conveyed forwards along the drill holes through pushing force provided by the pushing mechanism. When high-pressure water passes through the high-pressure hose at the front end of the high-pressure hard pipe and the self-propelled drill bit, high-pressure water jet is generated to conduct rock breaking dredging on collapsed and blocked portions, and self-propelling force is generated. The device is simple in structure, small in overall size and convenient to adjust, and can be conveniently used in coal mine downhole narrow working space. A whole power pipeline can be conveyed in long distance under joint acting force of pulling in front and pushing behind, and the pipeline can be prevented from being clamped. The hole flushing speed is high, efficiency is high, cost can be greatly reduced, and the gas extraction effect is improved.