The adsorption capacity of potassium chloride on the surface of clay and quartz sand, and that of potassium formate and ammonium formate on the surface of montmorillonite was studied. The inhibition effect of organic salt solution OS500A (containing 75% potassium formate) and OS500B (containing 75% ammonium formate), potassium chloride solution and clean water on the hydration and dispersion of clay was compared. The results showed that for potassium chloride solution, potassium formate solution and ammonium formate solution, the adsorption capacity of salt increased gradually with increasing concentration of salt solution. When the mass concentration of potassium chloride solution was 160 g/L, the maximum adsorption capacity of potassium chloride on the surface of montmorillonite, kaolinite and quartz sand was 5.6, 2.06 and 1.57 mg, respectively. When the mass concentration of formic acid brines approached 100 g/L, the maximum adsorption capacity of potassium formate and ammonium formate on the surface of montmorillonite was 5.51 and 5.42 mg. The adsorption of organic salt on montmorillonite was easily saturated, and its maximum adsorption capacity was equal to that of inorganic salt. The result of grain size analysis showed that four solution were arranged according to their inhibition ability on the hydration and dispersion of clay in following order: ammonium formate (OS500B)>potassium formate (OS500A)>potassium chloride 5%>clean water. If the wettability of rock surface was changed by kerosene, it would improve the inhibition effect of clay dilating by organic salt. The compounded system of potassium chloride and formic acid brines was applied in 10 wells of Fudong region，the protection effect was obvious.