The Xinzheng watershed in Zhongxian county, Chongqing, is a typical purple soil sloping ploughland in the Three Gorges areas. In 2009, the input-output budgets in this watershed is investigated and the results indicate that the nitrogen input is 918.26 kg/(hm2·a) and the output are 569.46 kg/(hm2·a). Furthermore, chemical fertilizer nitrogen is the main input source, accounting for 57.63%, and the main output track is nitrogen in crops, accounting for 36.22%. In this small watershed, the nitrogen loss load is 258.77 kg/(hm2·a). And the primary lost nitrogen is gaseous species, which is approximately 65.11% of the total lost nitrogen. In addition, nutrient nitrogen balance index is 3.4 in this watershed and the nitrogen surplus load is 348.80 kg/(hm2·a), much higher than the risk value, indicating potential occurrence pollution in ploughland.