Abstract: To evaluate the impact of saline-sodic agricultural drainage on water quality in vented area, the agricultural drainage of Qianguo irrigation area, Jilin province and Chagan lake was chosen as the studied object. In 2009 and 2010, during rice growing season, samples were collected monthly. K+, Na+, Ca2+, Mg2+, SO42-, Cl-, CO32-, HCO3-, total nitrogen, total phosphorus and chemical oxygen demand were recorded. Temporal and spatial variations of water quality from irrigation area to the vented area were analyzed. Water qualtity of Chagan lake was evaluated. The results showed that pH value in Chagan lake was larger than 7.8 at present. The maximum value of sodium adsorption ratio was 3.59 (mmolc/L)1/2, which appeared in May. The total nitrogen concentration was 1.22 mg/L, which was lower than the average value (1.56 mg/L) in the last 12 years. The content of total phosphorus was highest (0.28 mg/L) in June. In addition to chemical oxygen demand, the other indexes of water quality did not exceed the concentration limitations. However, in the flood season, Chagan lake belonged to the IV water quality type. This paper could provide the theoretical basis of ecological and environmental warning for Chagan lake.