The invention discloses a molybdenum disulfide nano-catalyst preparation method and catalyst which can be applied to a catalytic hydrogenation process of heavy oil. According to the preparation method disclosed by the invention, ammonium tetrathiomolybdate is utilized as a raw material and a surface active agent, the ammonium tetrathiomolybdate is dissolved into absolute methanol, then a reducing agent is added after the ammonium tetrathiomolybdate is mixed evenly, and the ammonium tetrathiomolybdate is put into a constant-temperature oven of 100 to 250 DEG C to be stored for 3 to 48 hours; the molybdenum disulfide nano-catalyst can be obtained after separation. The molybdenum disulfide nano-catalyst prepared through the invention has smaller size and uniform particle size. The molybdenum disulfide nano-catalyst prepared through the invention has a larger contact angle so as to have better dispersion in organic solvent, and catalytic performance of the molybdenum disulfide nano-catalyst in a catalytic process can be improved. According to the research, the MoS2 nano-catalyst is applied to the catalytic hydrogenation process of heavy oil for the first time. Furthermore, the preparation method disclosed by the invention is simple to operate, has moderate condition, low cost and a simple synthesizing device and can be hopefully applied to industrial production.