In view of the erosion damage of cement stabilized aggregate to highway base course, the influence of different fly ash content on the erosion performance of cement stabilized aggregate are studied by erosion testing. The results show that mixing with a certain amount of tly ash can signifi-cantly improve the anti-erosion performance of cement stabilized aggregate, and the optimum mix a-mount is about 10%. For the optimum mix amount, Ca(OH)_2 of cement hydration formation can re-act well with fly ash to produce a large number of gelatin. The gelatin can make the overall structure denser and the cohesive force can be enhanced. Therefore, the cement stabilized aggregate mixing with fly-ash would have a good integer and the anti-erosion performance can be improved