Rock salt is a versatile basic chemical raw material. Ordos Basin is not only rich in oil and gas resources, and Ordovician stratum in the east edge of the rock salt is one of the main salt basins also rich in resources. With the development of drilling technology, deep and ultra-deep drilling is more and more in complex formations; the higher demand of drilling fluid performance is increased. The paper introduced the case of well S/D-2: complex salt gypsum formation was encountered when drilling to the depth of 2480m, sticking happened with the enlargement of well diameter caused by salt dissolution and crystallization by salting out. According to these problems, drilling fluid system of polysulfonate under saturated brine was applied, borehole instability in salt gypsum formation, drilling fluid contamination and other technical issues were solved.