【英文摘要】Uncertainty is an important essential characteristics of nitrogen behavior in field and in processes of nitrogen diffuse pollution. According to the subject research plan, the natural spatiotemporal variations of soil nutrient contents in the paddy soil with zero tillage were measured and analyzed. Results showed that the spatiotemporal variability of the soil nitrogen and phosphorous contents are resulted from the combination of both the stochastic and tracking factors, and their variation direction (increase or decrease) is closely related to clay content in the paddy soil. However, the variation of the content of soil organic matter (OM) is not related to the variation of soil nitrogen content due to all paddy soil sampels have quite high OM in the research area. In the view of soil nitrogen lose rate and nitrogen export from the fields, soil nitrogen migration and transformation process in paddy field is more strongly effected by human activities such as land use type and farmland management practice, and natural hydrologic cycling, etc. We expanded our researches to the catchment (or watershed) scale for the nitrogen migration and its simulation uncertainty analysis in the research project. We find that the most important factor to influence soil nitrogen migration is water cycling. TN and TP export from field and into the river were significantly increased with runoff (P<0.01). Results based on Monte-Carlo modelling showed that the Spearman Rank Correlation Coefficient（SRCC）for the rivers flow at the end of the reach is more than twice as much as the that value from other moddelling parameters in the simulation model. In the SWAT model, the most sensitive parameter to influence the soil nitrogen migtation is the SCS runoff curve number (CN2), next important factor is the nitrogen concentration in the runoff and background in the flow, but flow velocity and the comprehensive degradation coefficient are only small influences.