Abstract: To explore a green and efficient double-rice cropping system that simultaneously maintains stable yield, enhances productivity, and improves soil nutrient status, a field experiment was conducted based on a mixed cropping system of Chinese milk vetch and rapeseed. Five nitrogen (N) application rates were established: no N application (CK), conventional N application (150 kg∙hm⁻², N1MR), 20% N reduction (120 kg∙hm⁻², N2MR), 40% N reduction (90 kg∙hm⁻², N3MR), and 60% N reduction (60 kg∙hm⁻², N4MR). The effects of different N application rates under green manure mixed sowing on rice yield, dry matter accumulation and partitioning, and soil nutrient characteristics were investigated. The results showed that, compared with the N1MR treatment, the actual yield of early rice under N2MR treatment was significantly increased by 16.1% (P<0.05). In the late rice season, the actual yields under N2MR, N3MR, and N4MR treatments were significantly higher than those under N1MR by 12.5%, 8.3%, and 6.9% (P<0.05), respectively. The total actual yield of the two rice seasons under N2MR treatment reached 14.5 t∙hm⁻², which was significantly higher than that under the other treatments by 7.4%−22.9% (P<0.05). In the late rice season, compared with CK treatment, all treatments except N1MR treatment significantly increased dry matter accumulation (DMA) at all growth stages. During the heading−maturity stage, the DMA of early rice under N2MR and N3MR treatments were significantly higher than that under the other treatments, with increases ranging from 21.7% to 151.7% and from 57.9% to 107.0% (P<0.05), respectively. In addition, the DMA of late rice under N2MR treatment was significantly higher than that under CK treatment, with an increase of 40.3% (P<0.05). With respect to soil nutrients, compared with N1MR treatment, soil organic matter content under N2MR treatment was significantly higher at maturity stages for early and late rice by 23.3% and 14.9% (P<0.05), respectively. Compared with N1MR treatment, N4MR treatment significantly increased available potassium content by 109.0%, 57.8%, and 56.9% (P<0.05) at the winter incorporation stage, early rice maturity stage, and late rice maturity stage, respectively. Correlation analysis showed that actual rice yield was significantly positively correlated with soil total nitrogen content, available phosphorus content, and population biomass (P<0.05), and extremely significantly positively correlated with soil organic matter content and effective panicle number (P<0.01), while showing a significant negative correlation with soil pH (P<0.05). Overall, under green manure mixed sowing, a 20% reduction in nitrogen application (N2MR) effectively balanced yield improvement and soil fertility enhancement, representing a sustainable nitrogen management strategy for achieving high yield and high efficiency in double-rice cropping systems.