The invention discloses a preparation method of salicylamide derivatives shown in the formula 1. The preparation method comprises the following steps that 2,5-dimethoxyaniline is dissolved in an organic solvent and reacts with ethyl acetate of O-alkylacylsalicyloyl chlorine to produce N-(2-alkylacyloxyformoxy)-2,5-dimethoxyaniline; the N-(2-alkylacyloxyformoxy)-2,5-dimethoxyaniline reacts with R3OH in the presence of iodobenzene diacetate to produce 3-(O-alkylacylsalicyloylamino)-4,4-dialkoxy-2,5-cyclohexadienone; in an organic solvent (such as tetrahydrofuran, methanol and dimethyl formamide and especially such as dimethyl formamide), the 3-(O-alkylacylsalicyloylamino)-4,4-dialkoxy-2,5-cyclohexadienone undergoes a reaction in the presence of a hydrogen peroxide aqueous solution and an inorganic base to produce 5,6-epoxy-4,4-dialkoxy-3-salicyloylamido-2-cyclohexenone; the 5,6-epoxy-4,4-dialkoxy-3-salicyloylamido-2-cyclohexenone undergoes a reaction in the presence of a boron trifluoride ether complex to produce 5,6-epoxy-2-salicyloylamido-2-cyclohexenyl-1,4-dione; and the 5,6-epoxy-2-salicyloylamido-2-cyclohexenyl-1,4-dione is reduced into 5,6-epoxy-4-hydroxy-3-salicyloylamido-2-cyclohexenone (DHM2EQ) shown in the formula (1). The invention also relates to a preparation method of the 5,6-epoxy-4-hydroxy-3-salicyloylamido-2-cyclohexenone.