In view of the ecological deterioration caused by massive concrete wastes and the lack of natural aggregate resources, an experimental study on mechanical properties of recycled concrete and the technique for their improvement was carried out for the Xicheng Canal three-class waterway regulation project through preparation of the recycled concrete with different strength grades and different recycled aggregate contents. The results show that the content of recycled aggregates has a weak effect on the mechanical properties of C35 concrete and concrete with even lower strength, but has a large influence on C40 concrete and concrete with even higher strength. With an increase of the recycled aggregate content, the mechanical properties of the recycled concrete degrade. The mechanical properties of the recycled concrete can be improved by rationally determining the recycled aggregate gradation, mixing in natural aggregates, strengthening the recycled aggregates, and optimizing the mix ratio. The application of the technique to the Xicheng Canal three-class waterway regulation project has achieved large economic benefits.