The invention discloses a method for one-step synthesis of 3, 4-dimethylthieno[2, 3-b]thiophene. The method comprises 1) mixing thieno[2, 3-b]thiophene, substituted methane, an organic base and a catalyst, and carrying out a reaction process under conditions of pressure and protective gas, wherein the catalyst is rhodium carbon having rhodium content of 5wt%, and 2) separating and purifying the reaction system to obtain a product 3, 4-dimethylthieno[2, 3-b]thiophene. Under the pressure auxiliary condition, in the presence of the catalyst, under action of the organic base, groups at 3th and 4th sites of the thieno[2, 3-b]thiophene undergo a nucleophilic reaction to produce 3, 4-dimethylthieno[2, 3-b]thiophene. The reaction yield is 96% or more.