NOVELTY - A 3,4-ethylenedioxythiophene monomer is prepared by dissolving ethyl acetate and sodium sulfide in acetone according to mole ratio of 2:1, stirring at room temperature for 2 hours, evaporating solvent to obtain thio acid diethylester, dissolving thio acid diethylester in ethanol, adding sodium ethoxide at room temperature, slowly adding diethyl oxalate, heating, refluxing, and obtaining ethanol solution of 2,5-diethyl-3,4-dihydroxythiophene, wherein mole ratio of sodium ethoxide and ethyl chloroacetate is 2-2.2:1 and mole ratio of diethyl oxalate and ethyl chloroacetate is 1-1.2:1.    USE - Preparation of ethylenedioxythiophene monomer for solar battery material, solid capacitor, conductive ink, organic LED, electrochromic material, anti-static material, and electromagnetic shielding material.    ADVANTAGE - Ethylenedioxythiophene monomer is prepared over a short period of time, production cost is low, preparation of monomer is safe and reliable, and product yield and product purity are high.    DETAILED DESCRIPTION - A 3,4-ethylenedioxythiophene monomer is prepared by dissolving ethyl acetate and sodium sulfide in acetone according to mole ratio of 2:1, stirring at room temperature for 2 hours, evaporating solvent to obtain thio acid diethylester, dissolving thio acid diethylester in ethanol, adding sodium ethoxide at room temperature, slowly adding diethyl oxalate, heating, refluxing, obtaining ethanol solution of 2,5-diethyl-3,4-dihydroxythiophene, wherein mole ratio of sodium ethoxide and ethyl chloroacetate is 2-2.2:1 and mole ratio of diethyl oxalate and ethyl chloroacetate is 1-1.2:1, adding phase transfer catalyst to ethanol solution of 2,5-diethyl-3,4-dihydroxythiophene, heating, refluxing for 4-8 hours, distilling residual ethanol and diethyl oxalate, adding ethyl acetate, washing, removing ethyl acetate, obtaining 3,4-dihydroxythiophene-2,5-dicarboxylic acid dimethyl ester intermediate, dissolving 3,4-dihydroxythiophene-2,5-dicarboxylic acid dimethyl ester intermediate in dimethyl sulfoxide and mixed solvent of ethanol and water, adding decarboxylation reagent, heating to 115-130 degrees C, allowing to react for 2-8 hours, decompressing, and obtaining 3,4-ethylenedioxythiophene monomer.