The sediment characteristics of slope runoff are of great importance to study the slope surface erosion and sediment yield. In order to study the sediment characteristics and the dynamic processes of slope runoff, and to reveal the composite relations between sediment concentrations of slope runoff and the slope length and rainfall intensity, the artificial rainfall simulation were adopted based on the different combinations of slope length and rainfall intensity. The comprehensive analyses were used to analyze the monitoring data of 5 slope lengths (1, 2, 3, 4, 5 m) with 13 rainfall intensities under a designed slope (20°). The results showed that: (1) Under the different slope length, the correlations between sediment concentrations and the rainfall intensities were different. The increases of sediment concentrations were the most obvious with the increasing rainfall intensities in the slope length of 2, 3, 4 m, but the least in 5m. The linear correlation between sediment concentration of slope runoff and the rainfall intensity was better in the 1 m slope length, but its increasing slope was small. Thus, the slope length of 3m was the most suitable for studying the changes of sediment concentrations with different rainfall intensities. (2) The sediment concentrations of slope runoff decreased undulately with the duration of production flow. The fluctuating characteristic value of the sediment concentration was small and the fluctuating frequency was large in the slopes length of 2, 3 and 4 m, while with a large concentration and a small frequency in 1 m and 5 m slopes. The changing frequency of sediment concentrations of slope runoff was much higher than that in river flow. (3) There were significant correlations between the sediment concentrations of slope and the main hydrological elements and hydraulics characteristic parameters.The flow velocity, discharge and shear force were the important factors affecting the fluctuation of sediment concentrations. Because the starting velocity of sediment varies with different underlying surfaces, it is the key to measure the flow velocity and sediment concentrations timely, accurately and dynamically for the study of slope surface erosion and sediment yield processes.