The 3-nitrogen content and distribution of the fleet layer groundwater in Kunming basin was studied through the analysis of water quality in the research area.On the basis,this paper discussed the mechanism of the 3-nitrogen transferring,transforming and polluting from the following aspects: the pollution resources,geology environmental conditions and the groundwater exploitation.In conclusion,the 3-nitrogen pollution has become a common problem of the fleet layer groundwater of Kunming basin,to some extent;the 3-nitrogen input flux takes important role on the eutrophication of Dianchi Lake.