is connected with downhole mixed fluid pipe 6 in the well shaft through the flow channel system in the wellhead device the downhole power fluid pipe and the downhole mixed fluid pipe are connected with hydraulic jet pump 9 suction inlet 10 of the downhole hydraulic jet pump is located at the lower boundary of coalbed the power fluid of high pressure drives the downhole hydraulic jet pump to work through an optimized design of the flow channel cross section area of the downhole mixed fluid pipe along with a reasonable allocation of the quantity of the power fluid the mixed fluid containing coal dust is configured to flow upwards at a flow rate much greater than the sedimentation rate of oil reservoir coal dust thus able to reach the ground through mixed fluid outlet 3 on the wellhead device as the coalbed water containing coal dust is discharged with control the coalbed gas is able to continuously flow into the well shaft subsequently under the action of downhole flow pressure at the bottom of the well the coalbed gas moves along an annular space between shaft casing 5 and downhole power fluid pipe 7 through casing valve 4 of the wellhead device and eventually reaches.