It develops two sets of thick salt in the Kuqa foreland basin, which has a great influence on the evolution of subsalt reservoirs. The favorable reservoirs about 4000m-5000m deep which was several hundred meters away from the bottom of the salt body was found in some area based on the logging interpretation technique. A detailed study was done to unravel the formation of the favorable reservoirs subsalt based on the techniques of formation water salinity analysis, scanning electron microscope (SEM) and cast thin section analysis. The results indicate that: in the first stage, the high salinity formation water began to infiltrate and crystallized after the deposition of the salt in the early, which would cause the dropping of the porosity. In the second stage, the formation water salinity was lowered by the activities of the groundwater which caused the dissolution of the salt, then the porosity was released, leading to the formation of the favorable reservoirs. In the third stage, the hydrocarbon was charged and accumulated in the favorable reservoirs.