The underground water type of Beier depression is NaHCO3 with low salinity. The water contains many organic compounds such as soluble gaseous hydrocarbon, phenol and fat acid and Br, B and other trace elements. These organic compounds change regularly in the flowing direction of the underground water. The characteristics of water chemistry are obvious abnormal in two discovered oilfields. The data obtained provide a hydrogeochemical basis for the exploration and development of reservoirs through the prediction of hydrocarbon potential in the depression.