The most conventional vehicle pretensioner system consists of an internal gear pair with involute teeth.However,it has been well known that the corresponding gear pairs are relatively weak under the situation of impact Ioadings.To improve this phenomenon,a new pretensioning gear system with cycloid teeth rather than the involute ones was proposed,and dual cycloidal gear mechanisms were designed for satisfying geometric constraints and dynamic loading conditions.The simulations of the prototypes were conducted by LS-DYNA program and the experiments for a prototype were performed for a dynamic model with impact loading devices.The results show that the better operation and the smoother motion are confirmed in the proposed cycloidal gear system rather than the conventional one without interferences between gear teeth under the impact of a crash.