The biped-wheel unmanned platform has the obvious advantages of high flexibility, high maneuverability, well controllability, great promptitude, fine adjustability, and a low manufacturing cost. A novel structure of the walking device of a biped-wheel platform has been investigated in this study, which is similar to the structure of airplane undercarriage. The structure is a plane four-bar linkage mechanism, which is composed of a side link, a connecting rod, a bracket, and a hand-spike. Swing range of the walking device determines the obstacle-surmounting capacity of biped-wheel unmanned platform. Therefore, the swing range of the modified novel walking device is calculated through theoretical derivation. Afterwards, the obstacle-surmounting capacities of the biped-wheel unmanned platform, including the ditch-crossing and the stair-climbing, are investigated based on the kinematic and kinetic analysis. Relative to the common type, reliability of the modified walking device can be improved. The research would increase the development level of the biped-wheel unmanned platform and promote its application in military and industrial fields.