CSSA-1 is a polyamine-based shale inhibitor for drilling fluids. Its molecular chain contains amino groups and hydrophobic groups, which can reduce the hydrophilicity of clay surfaces and inhibit surface hydration. The amino part of this product can dissociate into positive ammonium ions, which can enter the interlayer of clay under the action of chemical potential difference, displacing inorganic cations, promoting dehydration of clay interlayers, reducing swelling pressure, and compressing the interlayers, effectively inhibiting clay hydration and providing excellent wellbore protection. It is suitable for various water-based drilling fluid systems, including freshwater and saltwater systems.