Abstract: Hydrochemistry in Dalai Nur Lake consists mainly of Cl, K and Na, is Cl_I^Na type of water. The hardness is low, the alkalinity is high, salt content is up to 5.62g/l, 2.7times higher than that of the Lake of the Changbai Mountain. The ion contents in Dalai Nur Lake water change with seasons, winter>spring>autumn and summer, except HCO₃^-. Even the same ion, its content has a little change in different places and depth of the lake, generally less than 1—3%. Water of the lake contains As, Cd and Fe. But Cr and other harmful elements are very little. Ions in the lake come mainly from bedrock and the Quaternary system. Ions in bedrock and soils are solved and leached by precipitation to enter water. Under the control of topography, the water containing these ions move to the lake area, to empty into the lake. Through the complex hydrological geochemical action of these ions in the lake, Ca, Mg and HCO₃^- are combined into non-soluble salts to be precipitated; ions of K, Na and Cl are relatively accumulated, forming Cl_I^Na type of water.