Abstract: The microbial-induced carbonate precipitation (MICP) is a cementation and solidification method for sand with environmental advantages. However, the bonding performance of MICP for tailings with different particle sizes, as well as its applicability within conventional backfilling processes under varying cementing solution concentrations and bacterial addition levels, remains insufficiently understood. In this study, a uniform proportioning experiment considering the influence of cement–sand ratio (CSR), cementing solution concentration (CSC), and the volumetric ratio of bacterial solution to cementing solution (VRBC) on the uniaxial compressive strength (UCS) was conducted, and a series of microscopic analyses were used to demonstrate microbial mineralization behavior. Results show that the UCS of microbial blended tailings backfill (MBTB) exhibits a general trend of increasing and subsequently decreasing with rising CSC and VRBC. The UCS of optimally proportioned MBTB exceeds that of conventional backfill without microbial addition and maintains stable long-term strength. Comparative analysis indicates that a CSC of 0.5 mol/L and a VRBC of 1:1 yield the most effective microbial bonding performance. Although the cementing solution alone suppresses UCS, the subsequent incorporation of microbes significantly enhances strength, confirming the critical role of microbial mineralization and cementation within the backfill. The optimal UCS values for MBTB prepared with coarse and fine tailings are 2.44 and 1.55 MPa, representing increases of 49.69% and 23.03% relative to conventional backfill, respectively, demonstrating superior MICP efficiency in coarse-grained tailings. Microscopic analyses reveal substantial mineralized calcium carbonate distributed within the backfill, effectively filling interparticle pores, improving compactness, and enhancing mechanical behavior. Compared with microbial cyclic grouting approaches, the preparation of MBTB through conventional mixing not only ensures mechanical performance but also aligns more closely with practical backfilling operations, providing substantial engineering value.