Qaidam Basin contains abundant and highly prospective brine potassium-lithium resources. However, with the continuous expansion of production capacity and ongoing development, the easily accessible high-quality resources in the shallow part are decreasing, so it is inevitable to go deep mining. Compared to the shallow section, the brine reservoir in the deep part of the salt lake is relatively poor in quality, with weaker and more unstable water enrichment, so it is very difficult to exploit. In order to find out the characteristics of deep brine reservoir in Beletan section of Qarhan Salt Lake, the planar distribution and thickness variation of deep brine reservoir in Beletan section were studied by analyzing the lithology and physical property data of borehole. The results show that the southeastern part of the study area has the thickest reservoir and the highest quality of rock salt reservoir. Three-dimensional modeling of the brine reservoir shows that lithium-rich brine is mainly distributed in the middle and northern part of the study area, and the lithium content in the southern part is relatively low. The second ore-bearing layer on the plane has a large thickness of rock salt and fewer interbedded silt and clay layers in the central part, which is beneficial to the extraction of brine.