According to the findings of traffic flow and biomechanics,a human body is considered to be a 2- DOF(Degree of Freedom) system with mass,stiffness and damping.A dynamic model of crowd- bridge coupling systemwith crowd being on the bridge is thus constructed.Moreover,the dynamic characteristics of the coupling systemaffected by the crowd are analyzed,and the dynamic response as well as the pedestrian- induced vibration parametersensitivity of the coupling system in different walking modes is investigated.The results show that (1) an additionalvibration mode of the coupling system may occur due to the presence of crowd; (2) crowd density and locationgreatly affect the dynamic characteristics of the coupling system; (3) the influence of walkers on bridge's dynamicresponse mainly depends on two factors such as whether the walking frequency is close to the vertical fundamentalfrequency of the structure and whether the crowd is of the same walking pace; and (4) both crowd density andwalking speed influence the dynamic characteristics of the crowd- bridges coupling system to different degrees.Theproposed model helps avoid the randomness of parameter selection for calculating the coupling vibration of crowdand structure.