Secondary sylviteafter the conversion of carnallite sediments showsthe characteristics of low bromine and high rubidium. It has important implications for the understanding of the sylvitedeposits formed by carnallite leaching and removing magnesium chloride to form sylvite. Taking the lower salt layer (ore-bearing section) drilled in ZK0707 mine as the research object, the main elements and trace geochemical analysis of the lower salt were studied. The changes in contents of trace elements Br, Rb, K and coefficient ofBr×1000/Clin carnallite indicate that the salt brine has undergone a stage of concentration and desalination. Thesequence ofthe lower salt from bottom to top is salt rock-carnallitite-sylvinite rock-salt rock, which is reverse to the evaporation and concentration of brine.The sylvinite rock is directly deposited on the carnallite layerand it shows the character oflow Br high Rb. The sedimentary metallogenic model of the Bagan sylvite deposit was confirmed. After the carnallite was deposited, the sedimentary alteration occurred through the plastic flowingand uplifting of the lower salt anticline, and the carnallite generated sylvite under the action of continental water leaching. So it plays an important role that the input of terrestrial water (fissure water) in the evolution and sedimentation ofthe ore-forming brine.