To prevent a long-span steel truss pedestrian bridge vibration problem, finite element model was established by analysis software ANSYS, studies on this pedestrian bridge’s vibration question were carried on by frequent spectrum analysis based on recorded data and modal analysis. It has determined the vibrating level. In addition, the reason for this pedestrian bridge’s vibration has been thoroughly analyzed from the pedestrian and traffic, and had dynamic response analysis of pedestrian bridges under the crowd of pedestrians walking load. Then the main reason which causes the actual vibration characteristic has been found. Thus these both gave the reasonable explanation to the vertical vibration and provided the reference for the similar structure’s dynamic performance research.