To clarify the effects of combined application of chemical fertilizers and Chinese milk vetch on the nitrogen uptake，utilization，and fate of nitrogen in the rice-soil system，the 15N cross-labeling technique was employed to label urea and Chinese milk vetch plants. Using no nitrogen fertilizer applicati on(CK)as the control group，the effects of chemical fertilizers alone(NPK)as well as combinations of Chinese milk vetch with varying amounts of chemical fertilizers(NPK+G，80% NPK+G，and 60% NPK+G)on nitrogen uptake and utilization by rice，the fate of nitrogen derived from both chemical fertilizers and Chinese milk vetch，and the sources of nitrogen absorbed by rice were evaluated. The results showed that compared to CK，all fertilizer treatments induced a significant increase in the nitrogen absorption capacity of rice. Specifically，the application of chemical fertilizer alone treatment increased nitrogen uptake by 34.57%，whereas combined treatments with chemical fertilizer and Chinese milk vetch enhanced nitrogen uptake by 18.09%-45.21% relative to CK. The apparent loss of nitrogen decreased by 11.11%-73.37% in the treatments of 20%-40% reduction of chemical fertilizer combined with Chinese milk vetch than that of chemical fertilizer alone treatment. The absorption and distribution ratio of nitrogen from chemical fertilizers and Chinese milk vetch were the highest in grains，followed by straw，and finally roots of rice plants. Under the combined application of chemical fertilizers and Chinese milk vetch，a 20%-40% reduction in chemical fertilizer application enhanced the nitrogen utilization efficiency of chemical fertilizers in rice，while simultaneously improving the nitrogen uptake capacity and utilization efficiency from Chinese milk vetch. The seasonal utilization rate of nitrogen from chemical fertilizers by rice ranged from 27.22% to 35.78%，with a nitrogen residual rate in soil of 17.89%-22.90% and a loss rate of 41.32%-54.89%. The seasonal utilization rate of nitrogen from Chinese milk vetch by rice ranged from 33.44% to 49.25%，with a nitrogen residual rate in soil of 36.59%-42.88% and a loss rate of 7.87%-29.97%. With a reduction in the amount of chemical fertilizer applied in the combined treatments，the rates of nitrogen utilization from both chemical fertilizers and Chinese milk vetch by rice gradually increased. Additionally，a gradual increase in the residual rates of nitrogen from both sources was observed，along with a progressive decrease in the nitrogen loss rates. The proportion of nitrogen absorbed by rice from soil across all the fertilizer application treatments ranged from 84.92% to 87.91%，with 5.76%-12.09% originating from chemical fertilizers and 0.00%-6.74% from Chinese milk vetch. In treatments incorporating the combined use of Chinese milk vetch，reducing the amount of chemical fertilizer resulted in a gradual decrease in the proportion of nitrogen absorbed from chemical fertilizers by rice，being concomitant with a gradual increase in nitrogen absorption from Chinese milk vetch. In conclusion，reducing the application amount of chemical fertilizer by 20%-40% and combining with Chinese milk vetch could reduce nitrogen loss，improve the utilization rates of nitrogen from chemical fertilizers and Chinese milk vetch，and thus promote the nitrogen uptake of rice.