The invention relates to the technical field of petroleum and gas industry downhole completion, in particular to an oil well dewaxing and descaling device. The device comprises a steel wire rope, a gravity packer, a reaction torque self-locking device, a screw motor and a tapered mill. The gravity packer comprises a hammer body, a rubber sleeve and a center pipe. The lower end of the hammer body is connected with a pressing cap, a circulating hole is formed in the pressing cap, the upper end of the center pipe is hung on the stepped surface of the inner wall of the pressing cap, the rubber sleeve sleeves the center pipe, the rubber sleeve is arranged between the pressing cap and a tray, and the tray is connected to the lower end of the center pipe. It is not needed to pull oil pipes out ofa well one by one or inject any chemical agent, the effect of dewaxing and descaling the inner wall of a casing pipe is good, the procedures are simple, the cost is reduced, no production layer is contaminated, and no oil pipes or other downhole tools are damaged.