The invention relates to a preparation method of a semimetal compound of metal platinum. The method comprises steps as follows: a platinum simple substance and a selenium simple substance are put in areaction container as reaction materials; the reaction container containing the reaction materials is vacuumized until the atmospheric pressure is smaller than 10 Pa; the reaction container containing the reaction materials is heated to the reaction temperature and subjected to heat preservation for a reaction at 600-800 DEG C for 24-100 hours; the reaction container after the reaction is cooledto the heat preservation temperature and kept for a certain time, and a reactant is obtained, wherein the cooling rate is 1-10 DEG C per hour, the heat preservation temperature ranges from 400 DEG C to 500 DEG C, and the heat preservation time until the reaction container is cooled to the heat preservation temperature lasts 24-100 hours; excessive molten fluxing agents in the reactant are separated from a PtSe2 single-crystal sample.