Abstract: Changes of the erosion type and the rill erosion process under simple rainfall is one of the key problems in soil erosion research.By placing rare earth elements(REE) on different soil depth across the slope,the simulated rainfall is applied to study the change of erosion type and the rill erosion process.The results indicate that the main erosion type is sheet erosion at the beginning of the experiment,and serious erosion happens after the rill erosion appears.Accumulated the sheet erosion amount and rill erosion increase with the rainfall time,and the increase rate of the latter is bigger than of the former.The ratio of sheet erosion to total erosion decrease and the ratio of rill erosion to total erosion increases with the time passing by.At the end of the experiment,the rill erosion amount reaches 2 to 4 times of the sheet erosion.In this paper,a new REE tracer method is proposed to quantitatively distinguish the sheet erosion amount and the rill erosion amount.Also it can be used to study the process from sheet erosion to rill erosion,and it would be a new method to study the erosion process on slope.