The 3R pseudo-rigid-body model of compliant mechanism is introduced.The kinetic energy equation and deformation energy equation of compliant bar is deduced by Matlab software symbolic operation.The dynamics model of the compliant bar under the action of end load by applying Lagrange equation.The centripetal force factor

the moment of inertia factor

and the Carioles force factor are obtained through characteristic radius factor and stiffness factor substituted into equations group

and mutual coupling effect of the angle variable are analyzed.The dynamic response curves and its configuration charts are obtained through the numerical solution of two order variable coefficient linear differential equations.It shows that the pseudo-rigid-body amplitude from 1-bar to 3-bar increases gradually and rod coupling reduces.The result shows that the dynamics equations of 3R pseudo-rigid body model are more practical and versatile for simulating the dynamics characteristics of compliant bar than 2R pseudo-rigid body model.