In order to scientifically and systematically evaluate the ecological benefits of soil and water conservation on expressways,the author took Guangchang-Ji'an high-speed project as an example to analyze the dynamic changes of soil and water loss area and its proportion,soil erosion amount and average soil erosion modulus in different prevention and control areas in different construction periods,to construct evaluation inde system for soil and water conservation ecological benefit and to evalute the soil and water conservation ecological benefit of the project with the help of the analytic hierachy process（AHP）and the comprehensive benefit index.The results show that soil and water loss occurs mainly in the construction period of the subgrade engineering,soil field,abandon slag field.After completing the project,the area of soil erosion and the average soil erosion modulus in the prevention and control regions are much lower than the project constructed before,and the comprehensive index of ecological benefit of soil and water conservation is 6.33,which indicates that soil and water conservation measures have significant benefits for the project.