To address the demand for rapid road repair and promote the resource utilization of boron mud (BM), a multi-modified magnesium oxysulfate cement (BMMOC) was developed. The novelty of this study centers on systematically elucidating the synergistic modification mechanism of BM, mineral admixtures, and polymers in the MOS system. Results reveal a critical “dual-regulation” effect of BM: at a 10% optimal substitution, the paste achieves an ideal working window (initial set 76 min, final set 185 min