The invention discloses a light guide plate and a preparation method thereof. The light guide plate comprises a light outgoing surface, a back surface and side surfaces, wherein the light outgoing surface and the back surface are arranged oppositely; the side surface is connected with the light outgoing surface and the back surface; at least one side surface is provided with a light incoming layer; the part outside the light incoming layer of the light guide plate is a PS layer; and the light incoming layer is composed of the following components in parts by weight: polymethyl acrylate, microporous hydroxyapatite, n-propyl silicate, cellulose triacetate, acrylonitrile-butadiene-styrene copolymer, ultrafine activated silica powder, polydimethylsiloxane, polymethylpentene resin, polytetrafluoroethylene, 4-octylphenol, ethylene bisstearamide, ethyene glycol, stearate, acrylic emulsion, polymethylphenyl silicone, thermoplastic polyurethane elastomer, dicalcium phosphate, polyethylene glycol, a stabilizer, and a composite antioxidant. Through mixing the components, the light guide plate is prepared, the stability is strong, the transmittance is good, and light loss can be reduced.