Abstract: Daihai Lake is a semi-saline-alkaline lake,which located in Inner Mongolia plateau of China,its geographical position being 112°33′31″—40″E,40°29′7″—37′6″N.Based on the results of the chemical and biological surveys of Daihai Lake in summer 1996,this study dealt with a trophic state assessment of water quality in 1996 and comparative analysis on the changes of trophic state during the process of water salinization.Chloride ion,pH and total alkalinity of the lake were gradually increased during the study period,which approach to the upper limit of 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 is regarded.