Abstract: Using grid and the hierarchical sampling method to distribute the places where these samplings were gathered, the spatial variation analysis for Nitrate content of 76 sampls for groundwater in Chengdu Plain was studied by Ordinary Kriging and Probability Kriging which are both geostatistical methods. The results show that Nitrate content (expressed with NO\-3\+-) of groundwater is as a whole lower at present, but in some areas it exceeds criterion, about 12 percent of areas did not reached the drinking water quality criterion (less than 10 mg/L) prescribed by WHO, approximately 5 percent not at the drinking water quality criterion (less than 20 mg/L) prescribed by the Chinese government. The obvious distribution character of Nitrate content of groundwater is the north area (7.38 mg/L) > the east area (5.72 mg/L) > the west area (3.91 mg/L) > the south area(1.51 mg/L); The Nitrate content in groundwater in three counties, Pengzhou, Pixian and Xindu, located in the north of Chengdu Plain is likely to surpass the criterion mentioned above, with the probability varying from 0.25 to 0.50, However, in Dayi county, Dujiangyan city located in the northwest of the Chengdu Plain, including Shuangliu county located in the south of the plain much little, the probability is less than 0.05. At the same time, a conclusion can be drawn that the ordinary Kriging represents spatial variation characteristic of Nitrate content, and the other method can preferably reflect the hazard extent of pollution arisen by using Nitrate fertilizer.

Key words: groundwater, nitrate content, spatial variability, Probability Kriging