The invention discloses a waterproof ring mounting assembly of a limit switch part assembling machine. The assembly comprises a feeding support, a waterproof ring air cylinder, a transverse push plate, mounting sliding rails, mounting sliding blocks, a sliding table air cylinder and a lifting assembly; the transverse waterproof ring air cylinder is mounted on a side plate of the feeding support; a piston rod of the waterproof ring air cylinder is fixedly connected with the transverse push plate; the two parallel mounting sliding rails are mounted on the back side surface of the transverse push plate; the mounting sliding blocks corresponding to a side plate are arranged on the side plate of the feeding support and are matched with the mounting sliding rails respectively; the sliding table air cylinder is mounted on the front side surface of the transverse push plate; and a loading lifting plate of the lifting assembly is mounted on a workbench of the sliding table air cylinder. In the manner, the assembly is compact in structure, runs stably and can replace workers for automatic loading, the labor is saved, and the production cost is reduced.