Abstract: Under the outdoor environment, changes of terrain and gravity situation of mobile robot can influence load distribution and sequentially make control precision of the slip ratio drop. For this problem, a slip ratio self-adaptive sliding mode control considering load distribution is proposed. First, the express of robot load distribution is built by space force system relation considering influence of terrain and gravity situation. Next, in the control of slip ratio, a sliding mode surface with integral is adopted to avoid the chattering influence in sliding mode control, and a self-adaptive adjustment law is used in switch control gain to reduce the influence of uncertainty factors. Finally, simulation results show the effectiveness of the control method.