Abstract: Rod milling sand (RMS)—a coarse sand aggregate—was recycled for cemented paste backfill (CPB) for the underground mined area at the Jinchuan nickel deposit, named rod milling sand-based cemented paste backfill (RCPB). The adverse effects of coarse particles on the transportation of CPB slurry through pipelines to underground stopes resulting in weakening of the stability of the backfill system are well known. Therefore, sulfonated naphthalene formaldehyde (SNF) condensate was used for the performance improvement of RCPB. The synergistic effect of solid content (SC), lime-to-sand ratio, and SNF dosage on the rheological and physicomechanical properties, including slump, yield stress, bleeding rate, uniaxial compressive strength (UCS), as well as mechanism analysis of RCPB, have been explored. The results indicate that the effect of SNF on RCPB performance is related to the SNF dosage, lime-to-sand ratio, and SC. The slump of fresh RCPB with 0.1wt%–0.5wt% SNF increased by 2.6%–26.2%, whereas the yield stress reduced by 4.1%–50.3%, indicating better workability and improved cohesiveness of the mix. The bleeding rate of fresh RCPB decreased first and then rose with the increase of SNF dosage, and the peak decrease was 67.67%. UCS of RCPB first increased and then decreased with the increase of SNF dosage. At the optimal SNF addition ratio of 0.3wt%, the UCS of RCPB curing for 7, 14 and, 28 d ages increased by 31.5%, 28.4%, and 29.5%, respectively. The beneficial effects of SNF in enhancing the early UCS of RCPB have been corroborated. However, the later UCS increases at a slower rate. The research findings may guide the design and preparation of RCPB with adequate performance for practical applications.