In the western Songnen Plain in China, the alkalization degree of water bodies is high in the limnic wetlands. Generally, pH is above 8.0, and the hydrochemical types belong to HCO32--Na+ . Through analysis on the basic saline variables such as CO32-, HCO32-, Cl-, Ca2+, Mg2+, SO42-, Na+ etc. and the composed variables such as (Cl-+ SO42-）/ HCO32-and Na+ /(Ca2+ + Mg2+), the relationships between different variables were found, and the discriminant function and critical region map based on the pH value are obtained, and the function could be applied as one of the significant study methods on the investigation of saline-alkaline water-body. The relative analysis shows that the correlations are different among different salt variables, and some of them reaches significant level (α =0.01). Specially, in the western Songnen Plain, the lithofacies material of soil is mainly formed by the weathering of basalt and granite, and they are deposited inside the plain through running water transportation, so the NaAlO2, Na2SiO3 and NaHSiO3 in them can react with water and carbonate to form soda, which leads to the high correlations between Na+ and CO32-, HCO32-, Cl-, SO42-, and the correlation between Na+ and Na+ /(Ca2+ + Mg2+) is the highest. Moreover, because of high evaporation, the salts that are in the groundwater is congregated on the earth's surface, the dissoluble salts (Cl-,SO42-) turn into lake, which accounts for the reason for the high correlation between Cl-and SO42-.