Abstract: Aiming at the shortcomings of existing wheel-footed robots in adapting to multiple terrains and efficiently switching the motion mode, a switchable multimodal wheel-footed robot(Sirius) structure and a wheel-foot switching method are proposed by combining the advantages of wheeled robots and footed robots. When the environment changes, the robot can switch between foot and wheel modes to adapt to different terrains of scenes. Based on the rigid-body dynamics model, the dynamics in wheeled and footed modes are modeled and analyzed, and the whole-body dynamics model of the robot is established. Based on the dynamics model of the robot, a model predictive controller(MPC) and a whole-body controller are designed, two wheel-foot balance transition strategies are designed for the process of the robot switching from wheel-balance to in-situ bipedal standing, and constraints involved in the process of wheel-foot switching are analyzed. Finally, it is verified that the motion control schemes of the robot in both wheeled and footed modes perform well in simulation and physical experiments. In complex terrains, the pitch and yaw angles of the robot are controlled within ±0.1 rad. In the wheel-foot switching experiments, the static switching is stably completed within 8 s, and the dynamic switching is completed within 4 s. The results show that the proposed structure and control strategy have a high degree of target achievement, and possess good practicality and environmental adaptability.