Abstract: A multi-mode omni-directional mobile robot capable of climbing stairs is designed to deal with some complex terrains that the mobile robots encounter when moving in outdoor environments, such as steps and stairs. By switching among different motion modes, the robot can move rapidly like traditional robots while possessing an obstacle-surmounting ability like legged robots. Firstly, the kinematics model of the multi-mode omni-directional mobile robot is analyzed and constructed. Secondly, the relationship between the obstacle-surmounting ability and the center-of-mass position of the robot is studied, and the maximum height of steps that the robot can climb over is calculated. Finally, a stair-climbing method is proposed. The experimental results show that the designed obstacle-surmounting method enables the multi-mode omnidirectional mobile robot to successfully and stably climb steps. The maximum height of the step climbed over is 20.94 cm, the maximum angle of the slope climbed over is 35°, and the minimum turning radius is 0 cm.