Employed different rates of hairy vetch(Vicia villosa Roth)to substitute chemical nitrogen fertilizer，to quantify the effect on citrus seedling biomass and nitrogen uptake and the contribution to citrus nitrogen nutrition，aiming to provide a scientific theoretical support for the chemical nitrogen fertilizer substitution by green manure in citrus orchard.Potted citrus seedlings and hairy vetch were used for the study，and five treatments were set up，including chemical fertilizer control(100%CF)，substituting 25%，50%，75% and 100%(25%GM+75%CF，50%GM+50%CF，75% GM+25%CF and 100%GM，respectively)，with four replicates for each treatment.The biomass，nitrogen content and 15N abundance of citrus root，stem and leaf were measured after 6 months growth in the greenhouse.The substitution of chemical nitrogen fertilizer by green manure significantly increased the biomass and nitrogen uptake in all organs of citrus，and they all showed significantly increased and then stabilized with the increase of the substitution ratio.Total biomass of citrus was the highest at 75% substitution，which was 107.5% higher than the control treatment，while total nitrogen uptake of citrus was the highest at 100% substitution，which was 45.1% higher than the control treatment.The contribution of green manure to nitrogen nutrition in all citrus organs increased with the increase of substitution ratio.The highest nitrogen contribution from green manure was found at 75%GM+25%CF and 100%GM treatments，in which 36.56% ～ 50.00% nitrogen in roots，35.03% ～ 46.81% nitrogen in stems and 34.52% ～ 50.72% nitrogen in leaves，respectively，were from green manure.In contrast，for 25%GM+75%CF and 50%GM+50%CF treatments，only 8.96% ～ 20.77% nitrogen in roots，9.47% ～ 19.77% nitrogen in stems and 7.82% ～ 20.94% nitrogen in leaves were from green manure，respectively.It was also found the nitrogen distribution to root would be increased，while to stem and leaf would be declined，with the increase of green manure substation ration.This study confirmed green manure utilization in citrus orchard could effectively substitute chemical nitrogen fertilizer，reduce the inputs of chemical nitrogen fertilizer and enhance citrus nitrogen nutrition.