Pedestrian dynamic load has begun to play the critical role in footbridge design stage due to its construction fashion of long span and more flexibility. However, impeded by the stochastic nature of pedestrian loading, how to calculate the response of footbridge due to pedestrian walking appears as a tough problem for consulting engineers. To develop an accurate and practical method for the calculation of pedestrian induced footbridge vibration, a time domain based stochastic load model for pedestrian walking force is first proposed and expressed in parameters of human instantaneous walking gait, which is followed by an extensive investigation into the distribution law of pedestrian gait parameters through site tests. On the former basis, also illustrated in this paper is the procedure to integrate modal force due to pedestrian walking, as well as the framework to perform a mode superposition transient analysis for footbridges vibration under pedestrian loading. Finally, taking 43# Bridge as an example, the reliability and practicability of this methodology is validated by comparing the results from numerical simulation and from the experimental test, as well as by values determined in accordance to worldwide guidelines for footbridge design.