In view of the situation that the highway slope of loess area is frequently damaged by rainfall erosion，the paper took rainfall erosion as a separate disaster species and expounded the destroy mechanics of rainfall erosion on loess slope.The accidental elements of destroy of rainfall erosion is very few. The degree of slope disaster threatened need to be predicted in advance so as to to take measures for project in advance.The paper researched to set up the evaluation method and evaluation procedure of rainfall erosion disaster vulnerability on highway slope of loess area and took erosion modulus as evaluation indexes.Through the analysis of value of each factor and calculation method in USLE equation of soil and water loss. It computered a erosion modulus of loess region. According to the level of vulnerability,the paper analyzed the vulnerability of rainfall erosion on slope and the ability of anti disaster. It is necessary that on the premise of prediction and early warning information to take corresponding preventive measures and to reduce and control the occurrence of disaster.