In order to investigate the effects of farming and anthropogenic activities on underground river during fertilization period in karst area,we collected 102 water samples in the upriver,downriver,and paddy fields of Qingmuguan underground river in Chongqing in May,2008.According to the ions change in the upriver,downriver,and paddy fields of the underground river in the monitoring period and the molar ratios of Na⁺,SO^2-₄,NO^-₃ to Cl^-,the water quality in the upper and lower reaches of the underground river is closely related to agricultural and industrial activities and SO^2-₄,NO^-₃ and Cl^-in the underground river respond well to the fertilization activity.The springs in the downriver are the main water resource of living and production for local residents,so,study of the water quality in the period may have a certain role and significance in the guidance of water security.