The invention discloses a decarboxylation method of 3,4-ethylenedioxy thiophene. The method comprises the following step of: decarboxylating 2,5-dicarboxylic acid-3,4-ethylenedioxy thiophene by taking metal phthalocyanine with the structure shown as a general formula (I) as a catalyst to obtain 3,4-ethylenedioxy thiophene, wherein M refers to Mg, Mn, Fe, Co, Ni, Cu, Ag or Zn; and R is independently selected from -H, -Et, -OH, -OCH3, -COOH, -COOEt, -NH2, -NO2, -CN, -F, -Cl, -Br, -I and -Ph. The yield of the 3,4-ethylenedioxy thiophene is high, a solvent used in a reaction is environmentally-friendly and low-cost water, and the catalyst is reusable. The method has the advantages of simple process, low cost, high yield and environmental friendliness, and is suitable for industrial production.