Abstract: Ground subsidence caused by coal mining could be sufficiently controlled using cemented coal gangue backfilling materials. In order to study the influence of fine gangue rate, cement content and mass concentration of slurry on the compressive strength of backfilling materials and optimize mixture ratio of backfilling materials. Response surface method was used to design an experiment with 3 factors and 17 proportions based on the single factor experiment, furthermore, the response surface regression model was constructed, and the optimal ratio was calculated, which could provide a scientific method for obtaining a reasonable proportion of filling materials in industry. The results showed that the influence of single factor on the compressive strength of backfilling materials was in order of mass concentration of slurry, cement content and fine gangue rate. The influence of interactions between fine gangue rate and mass concentration of slurry on compressive strength of backfilling materials in the early stage was slight, while the influence of interactions between cement content and mass concentration of slurry on compressive strength of backfilling materials in the middle and later stages was the greatest. The optimal ratio of backfilling slurry was determined by the results of model optimization as m (coal gangue)∶m (fly ash)∶m (cement)∶m (water) = 50%∶22%∶8%∶20%, and the fine gangue rate was 52%, The compressive strength of backfilling materials curing for 28 days was 5.07 MPa, and the error range of the verification test was about 2%, the model was accurate and reliable. The Ca(OH)₂ generated by cement hydration motivates the active substances of fly ash and coal gangue and generates ettringite (AFt) and calcium silicate hydrate (C-S-H) gels. The continuous growth of curing age plays a good role in connecting the cementing system, making the network structure more stable and effectively improving the compressive strength of backfill.