An innovative robot is designed. It can move in omni-direction on flat floor with three degrees of freedom in plane,and is also able to passively overcome obstacles of up to 4 times of its wheel radius within the 45 degree slope range. By using rectangle configuration,the four Mecanum motorized wheels is arranged on a climbing structure on each side which is consisted by double cranks and spring coupling. In order to find the conditions of the system with four Mecanum wheels to move in omni-direction,the motion model of the general system is put forward and the inverse velocity Jacobian matrix is analyzed. Then six typical layouts of four Mecanum wheels are illustrated and the optimal layout is picked out by calculating the Jacobian matrix rank of the six typical layouts. The kinematic model of the climbing structure is built and its parameters are optimized. Finally,the functions of the robot system including straight movement,lateral movement,zero turning radius and overcoming obstacles are simulated based on the virtual prototype technology. A well functioning prototype is designed and manufactured,and its performance is excellent.