Abstract: The pseudo-rigid-body body model of a planar crank-rocker four-bar compliant mechanism with flexural hinges is developed at first.A new method for calculating the driving torque is then obtained on the basis of the dynamic analysis of the compliant mechanism with flexural hinges,and it shows that the flexural hinges have impacts on the driving characteristics of the compliant mechanisms.The results of example indicate that the peak driving torque is minimized by modifying the stiffness and the unstrained positions of the flexural hinges.The torque reduction factor is calculated for optimally designed mechanism.