The invention discloses a paint spraying device for a gearbox. The device comprises a fixing support, a motor support is fixedly connected to the upper portion of the right side of the fixing support,and a motor is fixedly connected to the upper portion of the motor support; a worm is rotatably connected to the output end of the motor through a coupler; a rotation sleeve is rotatably connected tothe middle of the upper portion of the fixing support, a transmission gear is fixedly connected to the lower portion of the rotation sleeve, and the transmission gear is meshed with the worm; a vertical sliding groove is formed in the middle of the left side of the fixing support, a vertical sliding block is slidingly connected into the vertical sliding groove, and a sliding support is fixedly connected to the right side of the vertical sliding block; a rotation inner rod is rotatably connected to the middle of the sliding support. Compared with the prior art, the paint spraying device for the gearbox has the advantages that the device is simple in structure and convenient to use, during use, combined patient spraying is conducted through a paint spraying device body at the fixed positionand a paint spraying device body at the movable position, it is guaranteed that no dead corner exists after the surface of the device is sprayed, the service life of the gearbox is guaranteed, and the device is worthy of popularization.