Abstract: A bridge-type compliant mechanism with direct coupling for the intermediate drive mechanism of inchworm actuator is developed and its simplified model is also established.The stiffness equations are deduced according to Cas-tigliano's theorem and the natural frequency is derived with the compliant mechanism simplified as one DOF spring-mass system.The experimental tests of stiffness and natural frequency are carried out and the results are compared with the results of finite element analysis(FEA) and analytical method.The results show that the errors of the analytical model of stiffness and natural frequency are 5.5% and 14.1%,and the corresponding errors of FEA are 7.7% and 10.1% respectively.The experimental results show the validity of the analytical model FEA.In order to facilitate parameter optimum design in the initial design stage,FEA is used to study the influence of geometrical dimensions of the compliant mechanism on its static and dynamic performance.Then a simple optimum design procedure by changing geometrical dimensions to optimize static and dynamic performance of the compliant mechanism is presented.