Abstract: To analyze large deflections beams in compliant mechanisms,based on the Pseudo-Rigid-Body Model( PRBM),a 4R PRBM model was proposed for the large deflection beams with single inflection in compliant mechanisms. The characteristic radius factors of the model were determined via optimization with minimum difference of inflections and the spring stiffness coefficients of the model were obtained by using a linear regression technique. The numerical result shows that both the tip locus and inflection point of the compliant link with single inflection can be simulated precisely by using the model proposed in this paper.