Abstract: A functionalized molybdenum disulfide nanosheet and its preparation method and application, where the preparation method includes steps below: mixing a solvent, 1 part by weight of lipoic acid and 5-10 parts by weight of a first compound for 2-4 h to obtain a mixture; adding 0.05-0.1 parts by weight of 1-hydroxybenzotriazole into the mixture, mixing for 24-48 h, and drying to obtain an intermediate product; performing ultrasonic treatment or heat treatment on a raw material-solution system to obtain a functionalized molybdenum disulfide nanosheet, where the raw material-solution system includes 5-10 parts by weight of the molybdenum disulfide nanosheet, 1 part by weight of the intermediate product and saline water, the first compound contains an ethylene oxide group and an alkylamine chain, the number of carbon atoms in the alkylamine chain is 12-18, and the number of the ethylene oxide group is 2-15.