Boron isotopic composition (δ11B) of evaporite in salt lake is indicative of palaeosalinity change of brine, but there is little study about boron isotopic compositions of carbonate deposition in salt lake system. In this study, we collected authigenic carbonate samples from ISL1A drilling core for analysis of boron content and boron isotopic composition. Results show that the boron content and isotopic composition of the samples vary from 10.88×10-6~265.66×10-6 and -1.28‰~+9.94‰ respectively, and they present a positive correlation. Analysis also reveals that the B isotope composition of brine increases with increasing of brine salinity of salt lake, which results in increasing of boron isotope composition of salt sediment. In the natural salt lake, inadequate sedimentary differentiation may result in carbonate deposition during evaporite precipitation, which possibly ran through all the stages of evolution of salt lake. Therefore, B isotopic composition of carbonate can be used to analyze salinity change of brine. Variation of boron isotope composition in carbonate from the ISL1A drilling core reflects ancient salinity changes and climate fluctuations in Qarhan salt lake since 41.8 ka.