Disclosed is a preparation method of a magnesium matrix composite reinforced with SiC particles, belonging to the technical field of metallurgical materials, including the following steps: (1) carrying out oxidation pretreatment on SiC particles; (2) laying a piece of magnesium alloy on a bottom, laying a layer of oxidized SiC particles, then repeating a laying operation of a layer of magnesium alloy and a layer of SiC particles until the magnesium alloy and the SiC particles are completely laid, introducing inert gases, heating and melting, then performing cinder scrapping; (3) cooling to a semisolid temperature of the magnesium alloys for semisolid mechanical stirring, heating, and mechanically stirring again; (4) cooling again to the semisolid temperature of the magnesium alloys, then casting into a blank; and (5) heating the blank to the semisolid temperature of the magnesium alloys and extruding to obtain the magnesium matrix composite reinforced with SiC particles.