Abstract: Coal gangue is the main solid waste derived from coal mining. Its disadvantages, such as significant quality fluctuation, high crushing value, large water absorption, and poor stability, limit the large-scale application of backfilling in goaf, which has become the technical bottleneck of resource utilization of solid waste in coal mines. Surface-strengthening treatment process of low-grade coal gangue using slurry-wrapping and powder-wrapping methods was explored. Pre-placed coal gangue cemented backfill (PCCB) was prepared using modified coal gangue and self-consolidating alkali-activated slag−tailings sand grout. Based on digital image correlation technology and acoustic emission technology, the effects of surface strengthening treatment of coal gangue on mechanical properties and uniaxial compression damage behavior of PCCB were studied. The results showed that both treatment processes significantly reduce the crushing value of coal gangue, thereby improving the mechanical properties of PCCB. The uniaxial compression failure mode of the PCCB specimen is mainly tensile failure. After the surface strengthening treatment of coal gangue, the crack initial rate and crack damage rate of PCCB are significantly improved, which can better resist crack growth during the compression damage process. When the coal gangue aggregate is treated by the slurry-wrapping method, the main influencing factor of the strength of PCCB is the crushing value of the modified coal gangue aggregate. The modified aggregate and the aggregate-matrix interface transition zone affect the strength of PCCB after the powder-wrapping method. The research results provide theoretical support and practical guidance for the application of PCCB in goaf backfilling, and open up a new way for green mine construction and resource recycling.