To address the issues of soil salinization in facilities and low efficiency of nitrogen fertilizer, pot experiments were conducted with eight treatments, including T₁ (conventional nitrogen application), T₂ (conventional nitrogen application with 15% reduction), T₃ (conventional nitrogen application with 30% reduction), T₄ (conventional nitrogen application with 100% reduction), T₅ (biostimulant + conventional nitrogen application), T₆ (biostimulant + conventional nitrogen application with 15% reduction), T₇ (biostimulant + conventional nitrogen application with 30% reduction), and T₈ (biostimulant + conventional nitrogen application with 100% reduction). The combined effects of biostimulants and nitrogen reduction on the salt tolerance traits and nitrogen utilization efficiency of rapeseed were studied. The research results demonstrated that the combination of biostimulants and nitrogen reduction significantly enhanced rapeseed salt tolerance and nitrogen utilization efficiency. The T₆ treatment (biostimulant + 15% nitrogen reduction) showed optimal performance, with rapeseed superoxide dismutase (SOD) activity reaching 519.66 U/g, while yield, dry matter accumulation, and nitrogen uptake were the highest among all treatments (202.90 g/pot, 60.87 g/pot, and 1.51 g/pot, respectively). This treatment also exhibited the highest nitrogen productivity (533.95 g/g) and agronomic efficiency (103.68 g/g), achieving the goal of “nitrogen reduction without yield loss”. No significant difference was observed between treatments with and without biostimulants in soil salinity. Compared to nitrogen reduction alone, biostimulants enhanced nitrogen utilization by strengthening the antioxidant enzyme system and optimizing soil carbon-nitrogen balance. These findings provide a scientific basis for nitrogen efficiency improvement in saline-affected protected farmland and promote the green, sustainable development of greenhouse agriculture.