Abstract: Based on the filed-tests of rainfall erosion to the four kinds of highway-slopes:slope without protection,grass sowing in thick nourishment,grass sowing in three dimensional network and platform tree-planting,this paper expounds the effects of rainfall on different kinds of highway-slopes in the following aspects:hillslope-runoff,mud content and slope erosion.From the tests,two conclusions can be drawn.One is that the process of rainfall erosion to highway-slopes can be described as follows:the raindrop first clashes the soil,and then the clod is dispersed and finally the slope is eroded.The other is that the most serious erosion to slope is due to the water from platform upside.In the end,the paper demonstrates that the effective ways to reduce the rainfall erosion to slopes are plant protection such as grass sowing in three dimensional network and in thick nourishment or platform planting.It also provides a reliable basis for the design of plant protection to highway-slopes in loess areas.