Abstract: During snow-melting（from March to April）and flooding（from July to August）in each year,the contents of main chemical components of lake brines in the mining area of the Xitaijinair salt lake are obviously lower than those in other months.The projected points of lake brines in binary system metastable phase diagram of Na+,K+,Mg 2+ /Cl-,SO 2-4-H2O are mainly around the invariant point of astrakhanite,schoenite and epsomite.But the salting-out degree in the Xitaijinair lake is higher than that in the new lake which occurs around the Kushuigou area.The projected points of lake brines in winter obviously are closer to the carnallite area in the phase diagram than those in summer,and the former has reached the stage of precipitation of sylvite.Analyses of chemical components of lake brines in the mining area in different time（in 2001 and from 2003 to 2005）show that the changes in chemical components in lake brines are still mainly controlled by seasonal change in surficial runoff,and at the same time the influence of human being on these changes is gradually increasing.