The 4th and 5th members of the Jialingjiang Formation and the 1st Member of the Leikoupo Formation in the northeast Sichuan basin host abundant brine resources rich in K, Li, B, and other elements, presenting significant potential for development and utilization. While it has long been assumed that the enrichment of K in Triassic brines in northeast Sichuan is due to the dissolution of potassium salt minerals in the strata, this hypothesis lacks definitive confirmation. In addition, research on the origin and evolution of Li and B in these brines remains limited. In this paper, the deep brine of Triassic in northeast Sichuan Province is taken as the research object. Compared to seawater, these brines exhibit significant enrichment in K+, Ca2+, Li+, and B, while Mg2+and SO2-4are relatively depleted. The 87Sr/86Sr and δ34 S values of the brine are consistent with those of the brine reservoir, suggesting in- situ formation through seawater evaporation and concentration. The Q- type cluster analysis shows that the chemical components of Bei 2 and CXD1 are similar, and the chemical components of C25, ZK601, HC1, and HC3 are similar. It is inferred that the enrichment of K in the brines of C25 and ZK601 is caused by the brine dissolving potassium salt minerals (polyhalite) in the formation. Dolomitization processes lead to the enrichment of Ca2+ and depletion of Mg2+ in the brine. The occurrence of sulfur and H2 S in the formation proves that a large amount of sulfuric acid is reduced, resulting in an obvious loss of SO2-4. The reduction not only elevates the δ34 S values of the brine and gypsum but also causes the δ34 S values of both gypsum and brine in the region to exceed those of contemporaneous seawater. During the late Jialingjiang Formation period, the eruption of rhyolitic magma in the Sanjiang area generated significant quantities of gases and hydrothermal liquids rich in Li and B, which were subsequently transported to evaporite basins. The δ7 Li and δ11 B values of Li and B in volcanic hydrothermal fluids and gases are relatively low. While these fluids increase the Li and B content in the brine, they also decrease the δ7 Li and δ11 B values, making them lower than those of normal seawater.