Through the analysis of the erosion characteristics of Mt.Mang loess and the coal ash on 25 slope, little runoff was found at the beginning of rainfall under the conditions of different materials and diferent rainfall intensities.As rainfall continued, runoff and sediment increased gradually and then reached sharply high values.After the process continued for a few minutes, they dropped to a steady state.The sharp value and steady time were very different under different materials and different rainfall intensities and occurred early when rainfall intensit y increased.Generally, the sharp value and steady time for sediment occurred 13 min less than runoff.In addition,the erosion characteristics of light coal ash are the same as those of loess under high rainfall intensity.