Abstract: Daihai Lake (112°33′31″—46′40″E,40°29′7″ —37′6″N) is a semi saline alkaline lake, which located in Inner Mongolia Pl ateau of China. Based on the results of the chemical and biological surveys of Daihai Lake in summer, 1996 and the survey of geography, hydrology and hydrobiology since 1950s, the author dealt with a comparative analysis on the changes of several relevant ecological factors from 1953 to 1996. Chloride ion, pH and total alkalinity of the lake were gradually increased during the study period, the concentration of chloride ion being 2306.1mg/L, pH 9.33 and total alkalinity 9.68meq /L in 1996, which approach to the upper limit for freshwater fish survival. According to above significant changes, the conclusion could be drawn that the process of salinization of Daihai Lake is getting strong. Also, in the study, the concentration changes of calcium and magnesium ion, ratio of calcium and magnesium, and total hardness was regarded.