The paper studied the nitrogen dynamic in rice-soil-leakage water system under different N application levels based on split supply in paddy rice field. The result showed that N uptake of rice increased quickly with the N application up to (225) kg/hm~2

and N uptake amount changed little when the applied nitrogen were more than 225 kg/hm~2. Nitrogen accumulation dynamic in soil showed that the long-term fertility for rice crop growth could not be sustained under 75 kg/hm~2 N application

but when N supply exceeded 225 kg/hm~2

a lot of surplus nitrogen was accumulated in soil. There was significant correlation between nitrogen applied levels with average total N concentration of the leakage water andcoefficient is 0.943. The period of booting stage to grain-filling stage is an important time for rice nitrogen uptake. N accumulation in soil increased quickly and the peak of N content in leakage water appeared after basal nitrogen applied

which implied that basal nitrogen fertilizer being more than 50% of the total applied amount may be the main reason leading to soil nitrogen accumulation and water pollution.