The salt- forming evolution of ancient salt lakes has periodic characteristics of multiple phases, continuity, and desalination- salinity- salinization. The systematic study of sedimentary rhythm fromthe salinization section is beneficial for thereconstruction of salt- forming evolution characteristics of ancient salt lakes. This paper investigates the salt- bearing section of borehole KL4 in the Kuqa basin and its 74 halite samples, and divides the salt- bearing section into 4 salt- forming rhythms. On this basis, work on petrographic characteristics, geochemical analysis of halite elements, and hydrogen and oxygen isotopes of halite fluid inclusions are carried out. The results show that (1) Ⅲ and Ⅳ salt- forming rhythms in the upper part of the section developed potassium, potassium- bearing halite, polyhalite, syngenite, glaserite and other salt minerals; (2) the distribution range of K+ content is 0. 021%~0. 158%, with an average value of 0. 051%; (3) the δ D and δ 18 O values of hydrogen and oxygen isotopes in halite primary fluid inclusions ranged from -78. 2‰ to -58. 7‰ and -2. 4‰ to 1. 3‰, respectively, with average values of -66. 32‰ and -0. 80‰, respectively; (4) the degree of evaporation and concentration of salt lake brine gradually increased from early to late, and the early salt- forming brine played a role in the pre- enrichment of the late high- concentration brine; (5) three potassium precipitation events were found in the third and fourth salt- forming stages. The results of this study provide an important basis for discussing the environment, sedimentary characteristics and salt- forming principles of Middle Eocene paleo- saline lake in the Kuqa basin.