Abstract: Modern agricultural practices are strongly linked to fertilizer application for maintaining optimum yields. However, inefficient fertilizer use has led to a significant portion of the nitrogen (N) applied to farm fields reaching surface or underground water and atmosphere systems. The scientists from all over the world are committing themselves on improving the utilization of N fertilizer and decreasing the N leaching and N₂O emissions from farmland. This paper aims to provide comprehensive management alternatives which can accommodate the needs to maintain high crop yields, to conserve diminishing natural resources, and to minimize environmental damage. The field experiment observations of N leaching, crop yields, etc., in conjunction with the local climate, soil and management information from winter wheat-summer maize rotation field, were utilized to test a process based model, Denitrification–Decomposition or DNDC, for its applicability for the cropping system, and then used the validated model to quantitatively evaluate the N loss in winter wheat and summer maize rotation croplands of North China. The optimum management practices were proposed with comprehensively consideration of the crop yield, N leaching, N₂O emissions and NH₃ volatilization. The results showed that the DNDC model could simulate the change of N leaching and soil residual NO₃^--N, NH₄⁺-N well in winter wheat-summer maize rotation field. Moreover, the model generally had acceptable performances in the model simulations for the yield of winter wheat and summer maize. According to the model’s simulation, the amount of N loss through leaching, N₂O emissions and NH3 volatilization were 49.4 kg(N)·hm^-2·a^-1, 17.71 kg(N)·hm^-2·a^-1 and 144.8 kg(N)·hm^-2·a^-1, respectively, in the management of traditional practices. Comprehensively analysis of the nitrogen losses, the authors put forward some optimum management practices for its applicability for local agricultural production conditions, which were to reduce 40% of conventional nitrogen fertilizer to 340 kg(N)·hm^-2·a^-1, to improve the 100% rate of corn straw returned to field, and to keep the conventional irrigation management practice. Compared with conventional management measures, the optimized management measures reduced 71.5% of N leaching to 14.1 kg(N)·hm^-2·a^-1, 15.8% of N₂O emissions to 14.91 kg(N)·hm^-2·a^-1, and 19.1% of NH₃ volatilization to 117.2 kg(N)·hm^-2·a^-1, and meanwhile maintained the crop yield. The evaluation results could be applied directly to the agricultural production practice.