In order to overcome faultiness and shortcomings of the existing clamping mechanism on non-standard mould, as a basis of load bearing on the mechanism, the arch frame structure was topological optimization designed with variable density method. Through analyzing and comparing the results of topology optimization from three manufacturing constraints, the adopted time of the “symmetrical and draft constraints” was finally found, and the arch frame had better morphological characteristics and manufacturability. moreover, its quality was reduced by about 55.5% compared with the original structure. the lightweight design of the mechanism was realized while improving material utilization ratio. The results of finite element static analysis showed that the arch frame optimized by topology was accorded with requirements of structural strength and stiffness design. In conclusion, the clamping mechanism could service two more years, and the damage of it was also less in the actual use process.