A wheel-track hybrid mobile robot with multimotion modes is designed. It is composed of a robot central body, four driving mechanisms, four independent track arms, two differential wheels, two guide wheels and so on. According to different environments, it can switch between the pure wheel mode and the pure track mode. A stability pyramid is defined by using a quasi-static model. The process of climbing the slope is analyzed with the stability pyramid method. Experimental results show that this hybrid mobile robot could fully possess the advantages of both the wheel and the track mechanism, achieving a good climbing slope capability.