A nano-organosilicon film-forming and hydrophobic shale surface hydration inhibitor is obtained by performing hydrophobic modification for nano-particles through long-chain organosilicon together with a surface-active agent. A preparation method of the said hydrophobic shale surface hydration inhibitor comprises steps as follows: nano-particles are added to the solvent under stirring conditions, and then an ultrasonic dispersion is performed; upon the end of the ultrasonic dispersion, the reaction system is adjusted to a pH of 9-11 to obtain mixed solution A; a long-chain organosilicon solution is then dropwise added to the mixed solution A for reaction under stirring conditions to obtain mixed solution B; a surface-active agent is added to the mixed solution B for reaction under stirring conditions; upon the reaction is finished, part of the solvent is removed to obtain the inhibitor.