This paper holds that the erosive rainfall in the arenaceous shale mountain lands is the magnitude of rainfall as well as rainfall intensity within 10 minutes based on the analysis and study of the observed and measured date fron the runoff plots.With an increase in rainfall and rainfall intensity within 10 minutes,the volume of soil eorded goes up.The testing results show that the weakness and strongness of soil erosion in arenaceous shale mountain lands depends on the magnitude of rainfall intensity within 10 minutes.