Abstract: The preservation and discharge of soil nitrogen pool and its growth and decline trend in the ecological systems of loess plateau were discussed with the following resulfs:1. The nitrogen preserved in the top soil ( 0-20cm ) was 1.5×108 tons, and 5.0×10⁸ tons in the layer reached by the plant roots ( 0-1m). The nitrogen preserved in soils of high-yielding crop land was 2 - 3 t/ha; 1.5-2.0 t/ha in moderate yielding soils and 1.0-1.5 t/ha in low yielding soils.2. The total input to soil nitrogen pools was 235×10⁴ tons, among which 57.0% came from chemical nitrogen fertilizer, 36.6% from organic manure. The total output ,of nitrogen was 250×10⁴ t, among which 69.6% due to harvest of crops, 12.8% due to erosion.3. Great effort should be made to increase nitrogen content by applying chemical fertilizers and organic materials because negative balance of soil nitrogen pool usually occured. Non-production oulput of soil nitrogen should be decreased in order to keep a dynamic equilibrium of soil nitrogen.