A deep potassium-bearing salt body is first discovered in the Simao basin and it is characterized by a cumulative thickness of 149 m and burial depths of more than 2350 m. In this study, Sr, K isotope from 15 sylvinites and Sr, S isotope of the 7 anhydrock have to be analyzed by MC-ICP-MS, respectively, and it aims to determine the material sources of the salt body. The results are shown that all of the 87Sr/86Sr ratios, δ34SV-CDT values, and δ41K values indicate that seawater provided potassium sources for this salt body. The 87Sr/86Sr values were negatively correlated with δ34SV-CDT and δ41K values, respectively, which revealed the presence of terrestrial freshwater recharge to the evaporation basin during the precipitation of salt. Freshwater recharge resulted in samples with 87Sr/86Sr values greater than parental seawater and δ34SV-CDT and δ41K values less than parental seawater. Data obtained by simulation calculation of the mixed source suggest that the proportion of strontium in the freshwater supply in the sylvinite ranges from 3.3% to 29.2%, and the proportion of strontium in the freshwater supply in the anhydrock does not exceed 35.2%. The Sr, S, and K isotopes compositions of the samples still hold characteristics of the seawater, because of terrigenous recharge amount is little and does not disturb the identification of parent source. This study integrates the traditional stable isotopes (Sr-S) with the emerging K isotopes to trace the source of deep potassium-bearing salt body in the Simao basin, providing reliable data to further investigate the genesis mechanism.