Method for mining coal and gas by hydraulic jet grouting washout

The invention relates to a method for mining coal and gas by hydraulic jet grouting washout, which comprises the following steps that a coal bed (10) is drilled to by using a large-diameter drilling machine; a coal bed gas mining well (1) capable of injecting water, discharging the water and venting is installed; well drilling cementation is performed by using a casing pipe (2); a well sealing device (9) is additionally installed; a ground water pump (5), a coal-water separating device (7), a gas mining device (8) and a fire retardant supply device (12) are installed; a jet grouting device (3) is lowered to the position of the target coal bed (10); high-pressure jet water provided by the ground water pump (5) acts on the coal bed (10) through the jet grouting device (3) to form a pressure relief space (11); the top and bottom positions of the jet grouting device (3) and the pressure of the jet water are regulated so as to control the coal bed mined range; a coal-water mixture reaches the coal-water separating device (7) through a drainage device (6); separated water enters the ground water pump (5) through the fire retardant supply device (12); the pressure relief space formed on the coal bed is washed to continuously generate coal bed gas; and the coal bed gas is conveyed to the gas mining device (8).