Brine from the saline Qarhan Lake was evaporated at 28 +/- 2A degrees C in a clean environment. Two groups of experiments were conducted; one with complete separation of precipitate and brine at different stages of evaporation, and the other with continuous precipitation during the evaporation. Seventy-nine precipitate and brine samples were collected during the experiments, and the Cl-37 values were determined using an improved thermal ionization mass spectrometry procedure for precise measurement of chlorine isotopes based on Cs2Cl+ ions. Based on the concentrations of Na+, K+, and Mg2+, evaporation was divided into three main precipitation stages as follows: halite dominant, carnallite dominant, and bischofite dominant. The Cl-37(solid) and Cl-37(liquid) values of the precipitate and coexisting brine samples at different stages showed the following characteristics. The precipitates were enriched with Cl-37 relative to the coexisting brine samples, and the Cl-37 of both the precipitate and brine samples decreased gradually during evaporation. The fractionation factors ( (h)) between halite and brine were the highest, followed by that ( (c)) between carnallite and brine, and then that ( (b)) between bischofite and brine. The (c) and (b) values of less than one, which indicate the precipitate is enriched in Cl-35, were found when the evaporation process entered a new stage. However, the Cl-37 values of carnallite, bischofite, and the coexisting brine samples decreased during evaporation. The residual brine is a Cl-35 reservoir. The experimental phenomena were consistent with the Cl-37 values in saline deposits in the literature. Cl-37 can be used as an indicator of brine evaporation processes, which is important in the exploration of sylvinite deposits.