The residence time of some elements in lake water is a very useful physicochemical parameter in the study of the behaviour,imigration,relative activity and aqueous sediments of chemical elements in the lake water of Qinghai Lake.Measurements of 13 elements and study on their residence time in both the lake water and river water indicated that.(1) the sequence of the residence time is;Cl >Na >K >B >Ni >Mg >Mn >Cr >Cu >Li >Al >Pb >Fe.and all of them samaller than those of sea water; (2) the longarithemic values of the residence time have well positive correlation to those of sea water;(3) the main factors that influence the residence time of the eletnents in the lake water are the concentration ration (C) and the hydration energy (L) of elements,and the logarithm τ_l have well positive correlation and negative correlation to the logari-Cr and L respectively.