Abstract: This paper mainly introduces the design and use of the assembly tooling of the double gear circlip with special structure, which is suitable for installation on the gear parts with internal and external teeth meshing.Compared with the traditional circlip groove structure, the circlip groove of the duplex gear is designed on the internal and external gears.After assembly, it is necessary to ensure not only the meshing of the internal and external gears, but also that the circlip is installed in the circlip groove of the assembly parts.Due to the special structure, it is impossible to assemble with circlip pliers.A set of assembly tooling is designed for the installation of this special structure circlip.The circlip is assembled in the circlip groove of the outer tooth in advance, and the assembly tooling is used to shrink the circlip to complete the assembly of the circlip.