The vertical dynamic interaction of pedestrian-bridge is studied by using biodynamic model. The biodynamic model adopts the stiffness-mass-damping (SMD) model expressed by pedestrian's step frequency and weight, under the assumption that the foot bridge is of Euler-Bernoulli model, and the control equation of pedestrian-bridge dynamic interaction in the vertical is established. The state-space method is used to solve the instantaneous model of non-proportionally damped system, and the time-varying frequency and damping ratio are obtained. The time-varying control equation is determined by using variable step four-level-five-order Runge-Kutta-Felhberg algorithm, and the dynamic responses of pedestrian bridge were compared with considering pedestrian-bridge vertical dynamic interaction and under the action of the pedestrian load. The calculated results show that with considering the pedestrian-bridge dynamic interaction in the vertical, the frequency of the foot bridge is lowered slightly, and the damping is increased significantly. When pedestrians walk at the frequency of foot bridge, the dynamic response with considering the Pedestrian-bridge dynamic interaction in the vertical should be obviously lower than that without considering pedestrian-bridge interaction.