Pseudo-rigid-body model is an important way to analyze kinematic and dynamic performance of compliant mechanisms and synthesize. The beam-flexible hinge combined mechanism is essential flexible fragment. A compliant mechanism was designed by using flexible fragments to replace rigid members of pseudo-rigid model. Traditionally pseudorigidbody model did not consider the effect of geometrical nonlinearity and deformation of the beam, so there was error between pseudo-rigid-body model of LEMs and the actual. In order to reduce the error, the impact of geometric nonlinearity was considered and corrected pseudo-rigid-body model was proposed, and in order to determine the applicability of pseudo-rigid-body model, the concept of pseudo-rigid factor was put forward. Flexible fragment can directly replace the rigid member when pseudo-rigid factor was in a certain range, and then the compliant mechanism can be obtained. Finally, the LEMs were optimally designed based on pseudo-rigid factor for cell engineering by ant colony optimization algorithm for continuous space.