The invention provides a preparation method of cardanol glycidyl ether with a high epoxy value. The preparation method comprises the following steps: a. preparation of hydroxy epoxidized cardanol, namely, reacting 100 parts by weight of cardanol, 60-200 parts by weight of epoxy chloropropane and 1-3 parts by weight of benzyltriethylammonium chloride serving as a catalyst at the temperature of 70-90 DEG C for 3-4 hours, cooling to 50-60 DEG C, dropwise adding 40-60 parts by weight of sodium hydroxide solution with the mass fraction of 30%, and carrying out ring-closure reaction for 2-4 hours, thus obtaining the hydroxy epoxidized cardanol; b. the side chain double-bond epoxidation of the hydroxy epoxidized cardanol, taking 100 parts by weight of the hydroxy epoxidized cardanol, 15-45 parts by weight of glacial acetic acid, 30-70 parts by weight of strong acid catalyst and 100-300 parts by weight of methylbenzene, controlling the temperature at 50-70 DEG C, dropwise adding 70-120 parts by weight of hydrogen peroxide with the mass fraction of 30%, and reacting for 6-8 hours to oxidize side chain double bonds of hydroxy epoxidized cardanol into an oxygen-bearing three-membered ring, thus obtaining cardanol glycidyl ether with the high epoxy value in the end.