Yiliping is a dry salt flat in the Qaidam Basin, which is characterized by lithium- rich brine deposits. Relatively little attention has been paid to the past composition and evolution of the brine during the mineralization process. In this paper, the samples of salt rocks were collected from the central drilling core of Yiliping. In order to obtain the composition of ancient brine during the salinization period since the Pleistocene, the chemical compositions of primaryfluid inclusions in halites were analyzed using laser ablation inductively coupled plasma mass spectrometry (LA- ICP- MS). The results show that the concentrations of Li, B, and K in the lower part of the section are higher than those in lower part of the section, indicating favorable conditions for the formation of Li- enriched brine in the lower part this section compared with the upper part. The Li, B, K and Mg concentrations of ancient brines are positively correlated. Combined with the variation of Ca concentration, it is shown that the main material source for forming the Yiliping Salt Lake is derived from the Nalingol River, and the contribution of deep fluids is insignificant. The evolution of each ion concentration in the halite fluid inclusions is consistent with the sedimentary rhythm and the paleoclimate changes, thus confirming that the composition of the salt lake brine is affected by paleoclimate ie, a dry and cold climate is more favorable for the formation of lithium- rich brine.