The utility model relates to a special screw pump device for coalbed methane, which comprises a sleeve and an oil pipe, and the lower end of the oil pipe is sequentially connected with a screw pump, an anchor, a water-gas separator and a screen pipe; a polish rod is rotationally arranged in the oil pipe and is fixedly connected with a rotor of the screw pump; a wellhead four-way joint is installedat the upper end of the sleeve, a connecting assembly is fixed to the upper portion of the wellhead four-way joint, and the upper end of the polish rod penetrates through the connecting assembly andis in transmission connection with a motor. A water outlet pipe is arranged on the side of the connecting assembly and provided with a first pressure gauge. A first horizontal outlet and a second horizontal outlet are formed in the wellhead four-way joint and are both communicated with a gap between the casing pipe and the oil pipe. The special screw pump device for coalbed methane is used for drainage of coalbed methane, has anchoring and water-gas separation functions, is good in anchoring effect, prevents equipment from rotating and moving up and down when in use, enhances the stability ofthe equipment, prolongs the service life of the equipment, and has the advantages of simple structure, high water pumping efficiency, convenience in maintenance and the like.