The Laos’s salt bearing Basin was located in the southeast of new Tethys domain during Cretaceous and hosted huge potash deposit during late Cretaceous. δ34SV CDT of anhydrite from borehole of Thakhek basin located in the southeastern Vientiane with value of 13.8‰~15.3‰ is similar to that of contemporaneous marine evaporites that indicated these anhydrites were with marine origin. These evidences further prove that the potassium materials in both the Laos’s salt bearing basin sourced from Cretaceous seawater with the mixture of fresh water from land. Combining with the update data that the time of potash deposition in both the Laos’s salt bearing basin and Simao basin was approximated and sulfur isotopic composition of Mengyejing Formation，we inferred that the sulfur isotopic composition in both the Laos’s salt bearing basin and Simao basin were consistent with that of contemporaneous sea water and proposed a preliminary scenario that the two basins were possibly connected when marine transgression happened.