The invention discloses a silicon carbide quantum dot and a preparation method thereof. The silicon carbide quantum dot is similar to a ball shape, the granularity of the silicon carbide quantum is normally distributed in the range of 2.5nm to 5.5nm, the excitation wavelength of the silicon carbide quantum dot is 250nm to 400nm, the emission wavelength is 350nm to 450nm, and the fluorescent spectrum peak is 380nm, 400nm and 420nm. The preparation method of the silicon carbide quantum dot comprises the following steps of mixing polymethylsilane and toluene solvent according to a mass ratio of 0.5 to 10: 600, heating the mixture in a high-pressure kettle to 500 DEG C to 600 DEG C through a program, and naturally cooling the mixture after preserving heat for 1h to 5h; and filtering the prepared toluene liquid containing the silicon carbide quantum dot, and freeze-drying or centrifuging the filter liquid at a high speed to obtain the silicon carbide quantum dot. The granularity distribution of the silicon carbide quantum dot is concentrated, the luminescence is strong and stable, and the preparation method is simple, easy and environment-friendly.