The utility model relates to a fan rotary retaining device of a motor outlet line tube, which mainly aims to resolve the technical problems that assembled pressure plate rotary retaining device has no beautiful appearance. The element of the technical proposal is that the base of outlet line tube is connected with a through hole of the outlet line tube on the chassis and the outlet line tube connected with a motor outlet line tube by through - hole of the outlet line tube and outlet line tube base. A connecting box is arranged on the upper of the outlet line tube and a square lug and a square hole cover plate is arranged. The square hole counterparts with outlet line tube link the square lug which is arranged at the square hole of the square hole cover plate. The objective to rotary retaining by welding the square lug on the outlet line tube of the motor is accomplished and within the square lug through square hole in the square hole cover plate. The structure is simple and beautiful and reliable, widely used by the fan motor outlet line tube installation.