The invention discloses molybdenum disulfide for a catalyst and a preparation method and application thereof. The preparation method is specifically that a molybdenum disulfide raw material is heatedand reacted under an aqueous vapor atmosphere to obtain the molybdenum disulfide for the catalyst having high catalytic activity. Sulfur defects are generated on a molybdenum disulfide plane by the etching action of aqueous vapor, and the catalytic activity of the molybdenum disulfide is greatly improved. The molybdenum disulfide catalyst prepared by the method has high catalytic activity, simpleoperation, low cost and high efficiency, and can truly realize the preparation of a kilogram-scale molybdenum disulfide catalyst. Chemical reagents that are greatly-harmful to the environment or highly-toxic are not used, the environment is not polluted, the production process is greatly simplified, the molybdenum disulfide for the catalyst is suitable for industrial production, has potential practical application value in the field based on the molybdenum disulfide.