Abstract: In view of the flexible structure feature of waist,a flexible two-wheeled mobile robot based on dynamics of flexible multi-body system is designed in this paper.Adopting the assumed mode method,we can Abstract the robot to a three-link robot system,and establish the flexible robot dynamics model using D' the Alembert-Lagrange,then we have obtained the system dynamics equation according to obliqueangles of the three poles and turn corners of two wheels as the parameters,and the system vibration equation of connecting rod with waist flexibility.The process of establishing the mathematics model is provided,and the simulation analysis of the model is conducted.The simulation results confirm that the model is efficient,and it provides a theory basis for the movement and the control research of the flexible robot.