Due to the lack of strength and easy shrinkage of cement stabilized recycled aggregate, the application of old concrete pavement crushing and recycling technology is limited. In order to improve the properties of cement stabilized recycled aggregate, this paper introduced steel slag and fly ash to study the synergistic effect, and analyzed the influence of different content of steel slag and fly ash on the mechanical strength and road performance of cement-based fly ash stabilized steel slag recycled aggregate (CFSSR). The results show that steel slag and fly ash have significant effects on the mechanical properties and road performance of recycled base materials. Specifically, with the increase of steel slag and fly ash content, the unconfined compressive strength and splitting tensile strength of CFSSR increase and then decrease. When the content of steel slag and fly ash is 50% and 16% (mass fraction), the 7 d unconfined compressive strength of CFSSR reaches the maximum value of 4.72 MPa, which is 25.20% higher than that of ordinary cement stabilized recycled aggregate. In addition, steel slag and fly ash also significantly reduce the dry shrinkage of the material, although the temperature shrinkage is slightly adverse, but the overall shrinkage is effectively reduced. Under the optimal content, a large number of needle-rod ettringite and C-S-H gel are formed in CFSSR, which interweave and fill the void, enhance the compactness of the structure, and produce a synergistic enhancement effect. This paper provides a scientific basis for the application of steel slag as base material in highway maintenance engineering.