Abstract: The resource utilization of coal-based solid waste is an important approach to alleviate its environmental pressure, and microbial mineralization technology is expected to further improve the mechanical properties and microstructure of the resulting cementitious material. However, the influence mechanisms of different microbial strains and cementing solution concentrations on the performance of coal-based solid waste cementitious material remain unclear. To this end, a cementitious material is prepared using coal gangue, fly ash, and cement; Sporosarcina Pasteurii (SP) and Bacillus Megaterium (BM) are incorporated, respectively; different cementation solution concentration gradients are set; and the macroscopic properties (fluidity, setting time, compressive strength) and microscopic characteristics (XRD phase, SEM morphology, DTG thermal stability) of the coal-based solid waste cementitious material are tested. The results show that with increasing cementing solution concentration, the fluidity and compressive strength of both microbial mineralization systems generally increase, the setting time shortens, and the amount of mineralized product increases. At a cementing solution concentration of 1.5 mol/L, the 28 d compressive strength of the SP system reaches 14.72 MPa and the 7 d precipitation amount is 4.15 g, both higher than those of the BM system (10.62 MPa and 2.87 g). The mineralized products of both microorganisms are CaCO₃, with calcite as the main crystalline phase; microstructural observation shows that the SP deposits are more continuous and dense, filling pores more thoroughly, while the BM deposits are relatively dispersed. DTG analysis shows that the SP system exhibits a major decarbonation peak from 760 to 770 °C, whereas the BM system shows continuous weight loss in the medium low temperature range, which intensifies with increasing concentration. SP demonstrates a stronger capacity to produce mineralized products and yields more significant performance gains. The research findings provide a reference value for promoting low carbon enhancement and parameter optimization of coal-based solid waste cementitious materials.