Provided are a quaternary ammonium salt and a preparation method and use thereof as an inhibitor, and a water-based drilling fluid and use thereof. The quaternary ammonium salt has a structure shown in formula I, wherein, in the formula I, R1 is selected from the group consisting of —H and —COOH; R2 is selected from the group consisting of —H and —CH2—COOH; R3 is selected from the group consisting of —NH—CH2—CH2—CH2—NH2, —NH—CH2—CH2—NH2, —NH—CH2—CH2—OH, —O—CH2—CH2—NH2, —N—(CH2—CH2—OH)2, and —O—CH2—CH2—NH—CH2—CH2—OH; and n and m are independently 10 to 15.