Abstract: Self-lock characteristics of the continuous alternate wheel and the mobile robot are described. The structure of the continuous alternate wheel is analyzed firstly. The friction of a locked wheel can be divided into sliding friction in radial direction as well as rolling friction and bearing friction in axial direction, which are measured by experiment. Then, self-lock characteristics of the continuous alternate wheel are introduced based on the frictions measured above. The self-lock areas of the wheel on paper and on carpet are 0～ 15° and 0～ 18° by experiments. At last, a mathematical force model of a self-locked robot on a slope is developed, and some experiments about the robot self-lock characteristics on the slope of different materials, i.e. paper and carpet, are carried out. The experiment results indicate that the smallest self-lock angles of the robot on paper and on carpet are 19.7° and 16.4° respectively when the angle between the robot coordinate and slope coordinate is 45°. Meanwhile, the biggest self-lock angles of the robot on paper and on carpet are 30.3° and 25.5° respectively when the angle between the robot coordinate and slope coordinate is 0.