The dynamic performance of elastoplastic beams system was investigated. Based on the nonlinear constitutive relation,the dynamics variational equations for an elastoplastic beam was established using virtual work principle, in which the geometric nonlinear effect was also taken into account. The assumed mode method was used for discretization, and then the kinematic constraint equations were used to derive the dynamic equations for multibody system. Simulations of single pendulum and double pendulum under gravity show the effect of plastic strain on dynamic characteristics of beams, leading to the increase of the absolute value of the average transverse deformation and the decrease of transverse vibration amplitude. Significant effect of plastic strain was revealed in case of sudden change of angular acceleration.