Abstract: The dynamic analysis of a wheel-legged robot with multiple drive modes is studied.Firstly,the vertical obstacle negotiation process is described,then the dynamic model for the process is built.The torque distribution between all motors,the influential factors of movement states and gravity allocation are included in the model.By means of the investigation of the whole process,the utmost states of two kinds of motors’ torque in the driving system are ascertained.The influences of different factors on the maximal output torques are analyzed and the method to work out the maximal height that the robot can rove through is brought forward finally.The result will provide a theoretical foundation to improve the robot’s adaptability in complicated environments.