To optimize the high-yield cultivation of Chinese milk vetch(Astragalus sinicus)in paddy fields and address the challenge of utilizing rice straw resources，a study was conducted to investigate the effects of rice straw returning and nitrogen fertilizer application on the growth，nutrient uptake of Chinese milk vetch，and soil fertility.The objective was to determine the appropriate ratio of rice straw and chemical nitrogen fertilizer application to provide a scientific basis.A double-factor experiment was conducted with varying levels of rice straw dosage 0(S0)，3000 kg·hm-2(half returned to field，S1)，and 6000 kg·hm-2(full returned to field，S2) combined with different nitrogen fertilizer dosages 0 kg·hm-2(N0)，45 kg·hm-2(N1)，90 kg·hm-2(N2)，and 135 kg·hm-2(N3).At the peak flowering stage of Chinese milk vetch，the yield of fresh grass，and nitrogen，phosphorus，potassium of plant were measured.The soil content of carbon，nitrogen in total organic matter and active organic matter including microbial biomass and granular organic matter in soil were analyzed.The results showed that the application of nitrogen fertilizer and rice straw incorporation was beneficial for increasing the fresh yield of Chinese milk vetch.Without nitrogen fertilizer input，the fresh yield of Chinese milk vetch decreased by 8.6% with high-rate rice straw incorporation.As the amount of nitrogen fertilizer increased，the increment in fresh yield of Chinese milk vetch with rice straw incorporation treatments gradually increased，with the largest increase of 21.3% observed in the N2 treatment with high-rate rice straw incorporation.Under the condition of half-rate rice straw incorporation，the fresh yield of Chinese milk vetch increased with the increment of nitrogen fertilizer，with the highest yield observed in the N3 treatment，which was significantly higher than other treatments.With high-rate rice straw incorporation，there was no significant difference in the fresh yield of Chinese milk vetch between the N2 and N3 treatments.Addition of straw of rice to the field significantly enhanced accumulation levels for nitrogen and potassium in the aboveground part of Chinese milk vetch，the application of nitrogen fertilizer increased the accumulation of nitrogen，phosphorus and potassium in the aboveground part of Chinese milk vetch.The combined application of nitrogen fertilizer with rice straw incorporation was beneficial for increasing the total nitrogen，inorganic nitrogen，microbial biomass nitrogen and particulate nitrogen in soil.Under the N2 treatment，with high-rate rice straw incorporation，the contents of total nitrogen，inorganic nitrogen，microbial biomass nitrogen and particulate nitrogen in the soil were significantly higher than those in the N1 and N0 treatments，with no significant difference from the N3 treatment.Overall，the interaction between rice straw incorporation and nitrogen fertilizer application had a significant effect on the fresh yield of Chinese milk vetch，the accumulation of nitrogen and potassium in the aboveground part，and the contents of microbial biomass carbon and particulate organic carbon in the soil(P<0.05).In conclusion，under the conditions of this experiment，a fertilization ratio with a rice straw returning amount of 6000 kg·hm-2 and nitrogen fertilizer usage of 90 kg·hm-2 was relatively suitable.This ratio was beneficial for increasing fresh grass yield，effectively utilizing rice straw resources，and improving soil fertility.