Abstract: Based on the measurement of nitrate nitrogen(NO₃^--N)contents of the groundwater,which is the source of drinking water of the rural residents in the northwest region of Lantian County,health risk assessment of the pollution was performed using the health risk assessment model available.The measurement shows that NO₃^--N concentration in the groundwater was on average 12.00 mg·L^-1 in the low-water season(March)and 15.81mg·L^-1 in the high-water season(September)and some of the water samples even exceeded the upper limit of GB 5719-2006(National Standard for Hygiene of Drinking Water)in NO₃^--N concentration in the groundwater decreased significantly with the depth of the wells,being the highest in the water within the depth of 0-20 m and much lower in the water below the depth of 60 m.The health risk assessment shows that the drinking water in Lantian County is higher in health risk in the Ba river valley and the tablelands in the southern part than in the mountainous area in the north.