Abstract: Filling mining can realize the coordinated development of coal mining and environmental protection. The material ratio has an important influence on the performance and cost of filling materials. The effects of cement content, fly ash content, mass concentration solid ratio and their interaction terms on the fluidity of filling slurry and the uniaxial compressive strength （UCS） of backfill are analyzed by single factor analysis method and response surface methodology, respectively. Slurry slump increases with the increase of cement and fly ash content, and decreases with mass concentration solid ratio. Slurry bleeding rate decreases with the increase of the three factors. The UCS of backfill increases with increases in cement content and mass concentration solid ratio, while increases first and then decreases with the fly ash content. The results of variance analysis of RSM models show that not only single factor had significant influence on performance, but also interaction terms have certain influence on performance. The response surfaces varying with the interaction terms are obtained. In the influence of interaction term cement content-fly ash content, the increase of the two factors weakens the influence of each other. In the influence of interaction terms cement content-mass concentration solid ratio and fly ash content-mass concentration solid ratio, the increase of the two factors weakens each other’s influence on slurry performance, but promotes each other’s influence on filling strength. Based on the analysis results of RSM, the reasonable material ratio is determined. The filling cost is saved, and the utilization of fly ash is increased, and better economic and environmental benefits are obtained.