Single-crystal platinum diselenide (PtSe2) is successfully synthesized through direct reaction of metal platinum foil and selenium powder under high pressure and high temperature. Characterizations are performed by scanning electron microscopy observation, X-ray diffraction technique and atomic force microscopy, which show that the largest crystallite size is more than 15 microns. Our studies not only lead to a new method for the growth of single-crystal PtSe2 under high pressure, but also provide a new technique and method in expanding the family of transition-metal dichalcogenides.