Rainfall runoff erosion transport capacity of high and steep slopes is an important scientific problem. The law of runoff erosion transport under the condition of the same rainfall intensity and different gradients and slope length was studied by indoor simulated rainfall experiment. The results showed that: (1) Under the test conditions, the flow depth was inversely proportional to the 1/3 power of hydraulic gradient and directly proportional to the 3/5 power of slope length, and the flow velocity increased in positive proportion to hydraulic gradient and flow depth. (2) Under the condition of bare slope with the same rain intensity, the runoff sediment concentration was directly proportional to the 1/2 power of hydraulic gradient, was proportional to the 4/5 power of the slope length. The sediment carrying capacity of water flow was directly proportional to the 1/2 power of hydraulic gradient. (3) The ratio of the turbulent diffusion effect of rainfall runoff to the effect of gravity was larger than that of open channel flow, indicating that the turbulent effect of raindrops is more obvious,the formula of sediment carrying capacity is given. Compared with the commonly used formula of river sediment carrying capacity, the coefficient was larger and the index smaller. The research results are of great significance for in-depth analysis of the mechanism of rainfall-runoff erosion and transport.