An epoxy impregnated resin and a preparation method thereof are disclosed. The epoxy impregnated resin is characterized by being composed of following raw materials in parts by weight: 32 to 35 parts of epoxy resin, 12 to 14 parts of terpolycyantoamino-formaldehyde resin, 2 to 3 parts of benzene dimethylamine tripolymer, 6 to 8 parts of phthalic anhydride, 1 to 2 parts of hydroquinone, 1 to 2 parts of tert-butyl hydroperoxide, 8 to 10 parts of methyltrichlorosilane, 1 to 2 parts of methyl tin mercaptide, 5 to 7 parts of styrene, 3 to 4 parts of vinyl carboxylate, 1 to 2 parts of nitrodracylic acid, 40 to 45 parts of xylene and 4 to 5 parts of film forming agent. The impregnated paint has the advantages of high temperature and high damp resistance, good electric insulation property, good toughness, high heatproof grade, and high mechanic strength. Heat conductivity of the impregnated resin is improved, so the expoxy impregnated resin can work at the temperature of 200 DEG C for a long term, and work at the temperature of 220 DEG C for a short term. The expoxy impregnated resin can be applied to the insulation systems, which have high requirements on heatproof grade, of motor train units motors and subway motors.