An 11-year(from 2008 to 2018) green fertilizer experiment was conducted to study the effects of different application amounts(15 000, 22 500, 30 000, 37 500 kg/hm2) of Chinese milk vetch with 20% N and K reduction on double cropping rice yield, nitrogen use efficiency and soil nitrogen. The results showed that compared with no fertilization treatment, the yields of early and late rice were significantly increased by fertilization, and the yield sustainability indexes were increased. There was no statistical significance in the 11-year average yield and yield sustainability index between the treatments of 20% N and K reduction with Chinese milk vetch and the single fertilizer application treatment. Through the analysis of the data from 2018, compared with the treatment of the conventional fertilization of local, the treatment of the N and K reduction with 30 000 kg/hm2 Chinese milk vetch significantly increased the early rice biomass and N accumulation, fertilizer N uptake and utilization efficiency(recycling and utilization efficiency, agronomic utilization efficiency, partial productivity), and late rice straw biomass, the amounts of accumulated N of rice, total N uptake and utilization efficiency(recycling and utilization efficiency, agronomic utilization efficiency, physiological efficiency, partial productivity). Applying Chinese milk vetch with appropriate N and K reduction could increase soil total N and alkali-hydrolyzable N, and effectively improve soil fertility. In summary, the treatment of 20% N and K reduction with 30 000 kg/hm2 Chinese milk vetch was optimal for the double cropping rice yield and nitrogen utilization.