Abstract: lop length is one of topographical factors determining soil erosion intensity.As one of important indexes in the Universal Soil Loss Equation(USLE),the slop length factor(L) reflects the relationship between slop length and soil loss,which has been used widely and studied deeply in soil loss prediction and soil and water conservation planning.The research progress of L factor at home and abroad was reviewed from the relationship between slop length and soil loss、the estimating methods of L factor,and extraction of L factor in geographic information system.Finally,five main problems of L factor in the study and application of soil loss prediction model in China were summarized,and the research trends were put forward.