Double- toggle clamping device plays a vital role in ensuring the working performance of large die- casting machines.However,the problems existing during the design of clamping devices,namely,various design variables and complex parameters,decrease the expansion force coefficient of the designed clamping devices and reduce the performance of the double- toggle.In order to solve these problems,a multi- body dynamic mathematical model is proposed for the optimal design of the clamping device of a 25MN die- casting machine,and the multi- body dynamic software MSC.Adams is employed to analyze and optimize the design parameters in the proposed mathematical model.The results show that,for the optimized clamping device,the expansion force coefficient increases from 18.93 to 23.59,the travel distance of the moving platen decreases by 17.4% and the clamping force increases to 32.27MN,and that the optimization reduces the impact force,improves the stability of the mould clamping and rea-lizes the energy conservation.Then,the strength check for the optimized design is carried out by means of numerical simulation.It is found that the design requirements are met.Finally,the optimized design is applied to the proto-type of a 25MN die- casting machine.