Abstract: Based on the pseudo-rigid-body model(PRBM),a new pseudo-rigid-body model with prismatic pair is proposed considering the effects of transverse deformation and axial deformation of flexible elements in compliant mechanisms.The prismatic pair and revolute pair describe axial displacement and lateral displacement of flexible element,respectively.The PR pseudo-rigid-body model of compliant mechanisms is set up.A three-dimensional optimization for the optimal characteristic radius factors and a linear regression for the spring stiffness coefficient are presented.The advantage of the new model is illustrated numerically through the comparisons with the 1R,2R models and compliant link.