A study of rill evolution process and sediment yield characteristics is important for rill erosion prediction model.At different slopes(10°,15°,20°and 25°)and different rainfall intensities(1.5and 2.0mm/min),the indoor simulated rainfall experiment with pure water was conducted to study the specific rill evolution process.The relationships between rill development stages and influencing factors were discussed.According to the characteristics of sediment concentration and rill form,the rill development process was classified as the four states of surface erosion,initial rill form,rill development and rill adjustment.Results showed that the proportions of sediment yield to the total erosion were different for different stages.The proportion for the rill development was the largest,about 40% of the total erosion.The duration for each stage changed with slope.Increase in rainfall intensity had a promotion role in rill and interrill flow velocities. Rill flow velocity was 0.75～1.77times of interrill velocity.Rainfall intensity and slope had a great influence on erosion rate.The relationship between flow velocity and erosion rate was closer on the same slope,but the quantitative relationship should be explored further.