A process for the preparation of an isothiocyanate compound of formula, A-N=C=S in formula I: -N=C=S is isothiocyanate group; A is -XRi or -CR 2 R 3 R 4, wherein X is -(CH 2) n -, and n is an integer of 0-6; R 1 is selected from the group consisting of methyl, tert-butyl, isopropyl, methylthio, methoxy, allyl, methallyl, cyclohexyl, methylsulfinyl, naphthyl, methyl cyclohexyl, morpholinyl, diethylamino, benzoyl, ethoxycarbonyl, tert-octyl, chlorine, trimethylsilyl, substituted or unsubstituted phenyl; wherein, the "substituted" means that one or more hydrogen in the group are substituted by substituents selected from the following group: halogen, methyl, bromomethyl, ethyl, methoxy, nitro, azido, trifluoromethyl, difluoromethoxy, methylthio, cyano, trifluoromethoxy, trifluoromethylthio, tert-butoxycarbonyl, ethoxycarbonyl; R 2, R 3, and R 4 are each independently H, phenyl or C 1-3 alkyl; wherein the process comprises the following steps: A-NH 2 → dithiocarbamate → A-N=C=S in the presence of an organic base, ANH 2 reacts with CS 2 in organic solvent to obtain a first reaction mixture containing dithiocarbamate; wherein the organic solvent is ethyl acetate; in the presence of an optional base catalyst, adding desulfurizing agent to the first reaction mixture to carry out a desulfurization reaction so as to obtain a second reaction mixture containing isothiocyanate compound, the desulfurizing agent is selected from the group consisting of methyl chloroformate, p-toluenesulfonyl chloride, solid phosgene, elemental iodine, chlorosilane, chlorophosphate, dicyclohexylcarbodiimide, dicyandiamide, triphenylphosphine, di-tert-butyl dicarbonate, cyanuric chloride, or the combinations thereof; the second reaction mixture is purified by post-processing to obtain the isothiocyanate as shown in formula. -N=C=S is isothiocyanate group; A is -XRi or -CR 2 R 3 R 4, wherein X is -(CH 2) n -, and n is an integer of 0-6; R 1 is selected from the group consisting of methyl, tert-butyl, isopropyl, methylthio, methoxy, allyl, methallyl, cyclohexyl, methylsulfinyl, naphthyl, methyl cyclohexyl, morpholinyl, diethylamino, benzoyl, ethoxycarbonyl, tert-octyl, chlorine, trimethylsilyl, substituted or unsubstituted phenyl; wherein, the "substituted" means that one or more hydrogen in the group are substituted by substituents selected from the following group: halogen, methyl, bromomethyl, ethyl, methoxy, nitro, azido, trifluoromethyl, difluoromethoxy, methylthio, cyano, trifluoromethoxy, trifluoromethylthio, tert-butoxycarbonyl, ethoxycarbonyl; R 2, R 3, and R 4 are each independently H, phenyl or C 1-3 alkyl; wherein the process comprises the following steps: A-NH 2 → dithiocarbamate → A-N=C=S in the presence of an organic base, ANH 2 reacts with CS 2 in organic solvent to obtain a first reaction mixture containing dithiocarbamate; wherein the organic solvent is ethyl acetate; in the presence of an optional base catalyst, adding desulfurizing agent to the first reaction mixture to carry out a desulfurization reaction so as to obtain a second reaction mixture containing isothiocyanate compound, the desulfurizing agent is selected from the group consisting of methyl chloroformate, p-toluenesulfonyl chloride, solid phosgene, elemental iodine, chlorosilane, chlorophosphate, dicyclohexylcarbodiimide, dicyandiamide, triphenylphosphine, di-tert-butyl dicarbonate, cyanuric chloride, or the combinations thereof; the second reaction mixture is purified by post-processing to obtain the isothiocyanate as shown in formula. in the presence of an organic base, ANH 2 reacts with CS 2 in organic solvent to obtain a first reaction mixture containing dithiocarbamate; wherein the organic solvent is ethyl acetate; in the presence of an optional base catalyst, adding desulfurizing agent to the first reaction mixture to carry out a desulfurization reaction so as to obtain a second reaction mixture containing isothiocyanate compound, the desulfurizing agent is selected from the group consisting of methyl chloroformate, p-toluenesulfonyl chloride, solid phosgene, elemental iodine, chlorosilane, chlorophosphate, dicyclohexylcarbodiimide, dicyandiamide, triphenylphosphine, di-tert-butyl dicarbonate, cyanuric chloride, or the combinations thereof; the second reaction mixture is purified by post-processing to obtain the isothiocyanate as shown in formula.