Research on N variations in field surface water and soils, rules of N uptakes of rice and amounts of soil microorganisms in rice-duck ecosystem was conducted by field experiments. The results showed: (1)Compared with conventional paddy fields, total nitrogen content in surface water and soils increased appreciably in rice-duck complex ecosystem, and NH+4 content in the field surface water and soils and N uptake of rice increased significantly in rice-duck complex ecosystem, meanwhile NO-3 content in the field surface water and soils scarcely any changed; (2) Rice-duck complex ecosystem boosted significantly total N uptake of rice and 17.8% higher than that of conventional paddy fields. Correlation analysis revealed that the relation between N uptake of rice and NH+4 content was fitted with by a unitary quadratic equation; (3) Rice-duck complex ecosystem could increase significantly soil microorganisms amount, in which bacteria amount were largest, actinomyces amount took second and the fungi amount were least.