The solid waste (e.g coal gangue, coal fly ash, desulfurization gypsum, gasification fine slag, furnace bottom slag) is made into underground backfilling material, which not only controls surface subsidence, but also is an effective way to consume a large amount of solid waste. In this paper, the strength at different curing ages is taken as the response target, the proportioning experiment of desulfurization gypsum, gasification fine slag and furnace bottom slag is designed by response surface methodology. The experimental results were analyzed by analysis of variance (ANOVA), the strength regression models at different curing ages were established, the interaction and influence effects of three kinds of solid wastes on age strength are analyzed. It is concluded that the influence of desulfurization gypsum and gasification fine slag on the age strength of backfill specimens is negative, the influence of furnace bottom slag on early strength is negative, but the influence on 28-day strength shows positive effect. Through regression model prediction and experimental verification, it is concluded that the optimal ratio of solid waste for underground backfilling is coal gangue: coal fly ash: desulfurization gypsum: gasification fine slag: furnace bottom slag = 1:0.4:0.2:0.1:0.1. Then, the compression deformation and failure morphology evolution of the backfill specimens with the optimal ratio are analyzed, it can be known that the stress rebound characteristics can make the backfill unload slowly and avoid sudden bursting; The failure morphology of the backfill changes obviously in the compression process, and preventive and remedial measures can be taken in time according to the failure morphology. Finally, Mercury Intrusion Porosimetry (MIP) test was carried out on the pore structure of the backfill specimen with the optimal ratio, which showed that the pores in the backfill were mostly closed pores, with a pore size range of 5–3 × 105 nm, mainly medium and large pores, and the compactness was not high; The results of X-Ray Diffraction (XRD) and Scanning Electron Microscope-Energy Dispersive Spectromete (SEM-EDS) showed that there are few active components in the solid waste, and there is no hydration reaction between the solid wastes. The main minerals in the backfill specimens are gypsum, quartz, kaolinite, mullite and calcite. The content of hydration products of cement and solid waste are mainly thin rod-like ettringite and cotton-like and fibrous gel. Its content is less, so the strength of specimen is lower.