Abstract：In order to reveal the reason of Nitrogen lost in the agriculture irrigation process and the pollution to water environment,we take the BeiChang test area as the research object in Inner Mongolia HeTao irrigation area and based on the analysis of the field result, the impact factor and the law of Nitrogen lost in agriculture drainage in pre and post autumn irrigation recession was studied.,analysed the process of Nitrogen lost. The results show that the irrigation amount 、distribution of fitch and topography and geomorphology are the main impact factors of Nitrogen lost in agiculture. The Nitrogen lost will cause effectson surface water and groundwater. This paper obtain its migration law in surface and groundwater environment : total Nitrogen, ammoniacal Nitrogenconcentrations increased after autumn irrigation,totalnitrogenconcentration s increased gradually around the channel groundwater along the back water. Preliminary estimated the relation was 6:1 about Nitrogen lost amout 、subsurface filtration amount and surface lateral seepage in experiment.