A four-year stationary field experiment, using the lysimeter method, was conducted to investigate effects of application of nitrogen fertilizer and incorporation of straws on nitrate leaching in the soil layer, 90 cm in depth, in a field under wheat and maize rotation in Guanzhong Plain of Shaanxi Province. Results show that nitrate leaching varied sharply in a year and occurred mainly in July, August and September, the rainy season of the year, and could be observed after flood irrigation, too. The nitrate concentration in the leachate and nitrate leaching loss in the whole monitored period was 0~103.5 mg L^-1 and 0~21.8 kg hm^-2, respectively, and both displayed an increasing trend along with nitrogen application rate. The crops gained relatively high yields (14.4 t hm^-2 on average) in all the 4 years, when 330 kg hm^-2 N (150 kg hm^-2 N for wheat and 180 kg hm^-2 N for corn) was applied for the wheat/maize rotation system. Any further increase in nitrogen application rate did not bring about increase in crop yield, but enhanced accordingly nitrate accumulation in the soil profile and nitrate leaching loss monitored at the depth of 90 cm of the profile. Straw incorporation showed some yield increasing effect only two years later. Compared with Treatment N330, Treatment N330+S increased yield of the crops by 15.1% and 14.2% in 2010 and 2011, respectively. However, no significant effects were observed on nitrate accumulation and leaching. Regression analysis of the data exposed an positive exponential relationship of nitrate accumulation in the 0～100 cm soil layer and nitrate leaching loss with annual nitrogen application rate, which means that the higher the nitrogen application rate, the higher the nitrate accumulation, the higher the nitrate leaching loss, and the higher the proportions of the two to the total nitrate applied.