In order to study the nitrate source in shallow groundwater of Xi'an,the paper collected several samples of acquisition underground water from piedmont area of Qingling, suburban, urban of Xi'an,analyzed the conventional chemical index and nitrogen oxygen isotopes. It used the nitrogen and oxygen isotope model of nitrate,Isosource model to identify the main sources of nitrate in groundwater and the ratio every source.The results show that in urban area of Xi'an,the nitrate in groundwater is mainly from animal waste water and sewage, which accounts for from 55% to 75%. In the suburban area, the nitrate in groundwater is mainly from organic nitrogen of soil, animal waste and sewage which is from 37% to 55% and from 36% to 58% respectively. In the piedmont area of Qingling, the nitrate in groungwater is mainly from soil organic nitrogen and the rate is from 77% to 96%.