［Purposes ］ This paper aims to address the optimization problem of cementitious component proportions for flowable fill materials using recycled powder from asphalt mixing plants.［Methods］ This paper analyzed the influence of cement，fly ash，and slag powder contents on the workability （fluidity and bleeding rate ） and mechanical properties （7 d and 28 d compressive strengths） based on the response surface methodology （Box-Behnken design ）.Furthermore，the hydration mechanism was revealed through micro -tests including X -ray diffraction （XRD），infrared spectroscopy （IR），and scanning electron microscopy （SEM）.［Results］ The results indicate that fluidity is primarily dominated by the fly ash content，followed by cement and slag powder，and the cement -fly ash interaction significantly improves flowability at low and medium contents.The bleeding rate exhibits a nonlinear relationship with the cement content，reaching the minimum at a cement content of 6% and a fly ash content of 5%.Slag powder makes the greatest contribution to compressive strength，and its interactions with fly ash and cement are significant.Under the optimized proportion of cementitious components （the ratio of cement to fly ash to slag powder is 33∶26∶41），the model prediction error is less than 5%.The optimal proportion is determined as a ratio of recycled powder，cement，fly ash，and slag powder of 100∶7.28∶5.78∶8.99，with a water -solid ratio of 0.39 and a water -reducing agent of 1.7%.The comprehensive performance indicators are as follows：fluidity is 209 mm；bleeding rate is 3.93%；7 d compressive strength is 3.34 MPa，and 28 d compressive strength is 7.88 MPa.The hydration products of the flowable fill materials using recycled powder are mainly C -S-H gels，and the pozzolanic effect of fly ash and slag powder promotes the formation of C -S-H gels.［Conclusions ］ This proportion combines environmental protection and engineering applicability，providing experimental technical support for the design of flowable fill materials using recycled powder.