The contact force between pantograph and catenary commonly oscillate because of the elasticity distribution and the elastic wave disturbance. In order to investigate the later factor, a close form of the contact force variation is derived theoretically and verified by the FEM simulation. The results show that, when the incident wave passes through a moving pantograph which contacts with the elastic guide, the velocity of the wave guide at contact point, the running speed, and the mechanical impedance of both contact wire and pantograph collector have influences on the amplitude of contact force. The contact force increases or decreases depending on the wave guide movement trend, and the amplitude of variation depends on the wave guide velocity. Moreover, as an application of the study, the performance of the rear pantographs within multiple pantograph collecting current is analyzed thoroughly.