Abstract: The slope erosion is caused by slope landslide which is the important influence factor,so it is necessary to research the soil particle erosion mechanism and the influence factors. The soil erosion mechanism has been researched in the state of slope runoff by the theory of sediment transport mechanics. The relational expression has been obtained between critical erosion gradient with the main influencing factors. It has been found that the critical erosion gradient is not a constant,but a subject to the influence of these factors on the variable interval.