Abstract: To access to the complex and unpredictable environment where the ground may be soft or hard alternately, a transformable wheel/track robot was proposed, which could travel over relatively smooth terrain quickly and move on uneven terrain well. The robot consists of a control box unit, two symmetric transformable wheel/track units and a tail sting unit. In the paper, the system structure and key mechanical points-including the positioning method of the walking wheels, the four-bar linkage conversion mechanism and the retractable track were presented, and then the obstacle climbing ability was analysed. The result shows that, the walking wheels are fixed firm, and the four-bar linkage conversion mechanism and the retractable track can quickly switch between in wheel mode and track mode, and the robot can successfully cross steps and stairs,which would lay the foundation for researching new mobile mechanism and wheel-track mechanism technique.