Abundant brine lithium resources exist in the Qaidam Basin, presenting a favorable prospect of exploitation and utilization. As the two most significant types of lithium brine in the Qaidam Basin, the salt lake brine in the central area of the basin and the structural fissure-pore brine in the western anticlinal structures of the basin are examined. The hydrochemical characteristics of them were compared and analyzed. Based on the systematic analysis of ion correlation, ion characteristic coefficient, and H-O and B isotope composition, the causes thereof are discussed. Studies have indicated that there are marked differences in hydrochemistry between the two types of brines. The salt lake brine presented a relatively high average total dissolved solid content (320.1 g/L) and LiCl content (1378.33 mg/L), while the major ions were relatively abundant in K+, Mg2+, SO2- 4 and deficient in Ca2+. The average total dissolved solid (186.4 g/L) and LiCl content (376.04 mg/L) of the structural fissure-pore brine are relatively low. Meanwhile, significant differences exist in different anticlinal tectonic regions. The ionic components are relatively abundant in Ca2+ and deficient in K+, Mg2+, SO2- 4. The analysis of ion correlation, ion characteristic coefficient, H-O and B isotopes suggests that the two types of brines might have the same origin and have undergone distinct evolutionary processes, which are the two remnants of the evolutionary decline of the ancient lake in Qaidam. Salt lake brine is the evaporation residual brine. With the migration and evolution of the ancient salt lake, salt lake brine underwent continuous evaporation and concentration, and eventually enriched and formed in the central basin. The structural fissure-pore brine is the secondary salt lake brine that was sealed during the disintegration of the ancient lake, and it undergoes the transformation of leaching after being sealed, thus having the dual genetic characteristics of evaporation residual brine and leaching brine.The disparity in the evolution process of the two types of lithium brine gave rise to different brine lithium resource endowments in the Qaidam Basin.