Abstract: This paper developed a novel nano-silica fume-modified phosphorus slag micro powder (referred to as NPS). The effects of NPS on slurry microstructure, rheological behavior, and mechanical properties were systematically investigated by means of particle surface water film thickness, SEM, cement hydration heat analysis and XRD. Experimental results show that NPS, as a mineral additive, can finely regulate the packing density of slurry structure particles and refine the pores. When the dosage of NPS is 8%, the 3-day compressive strength of cement mortar is 6.3% higher than the pure cement. At a 10% dosage, the shear stress, plastic viscosity, and yield stress of cement paste increase by 68%, 121%, and 193%, respectively. These improvements in rheological properties and early-age strength highlight the potential of NPS as an effective early-strength plasticizer for 3D-printed concrete, offering significant prospects for industrial applications,and also provide a new way for the comprehensive utilization of phosphorus slag under the background of 'double carbon'.