Abstract: In the third opening of the well AT40 area, "salt gypsum layer" was encountered. For the balance of "salt gypsum layer" formation creep, the density of drilling fluid was up to 1.65-1.70 g/cm³. In order to avoid pressure leakage and differential pressure sticking risk in the low-pressure formations such as Cretaceous, Jurassic, Triassic and Carboniferous during the same opening, pressure plugging was demanded. Due to long opening hole and complex formation lithology, problems existed for pressure sealing. Besides, while drilling in the "salt gypsum layer", controlling the creep rate of "salt gypsum layer" to satisfy the requirement of casing, and the good rheological properties and anti-collapse performances of high-density and under-saturated saltwater polysulfonate system were the difficult points of drilling fluid technology. Aiming at the complicated situation in this area, taking the measures of plugging while drilling, sectional bearing, reasonable selection of drilling fluid density, optimizing drilling fluid rheology, we solved the difficulties of pressure sealing on the salt layer and the technology of drilling fluid through salt layer in the well AT40 area.