The present invention discloses two dithieno[2,3-b:2',3'-d]thiophene preparation methods. The method 1 comprises: adopting 2,3'-dibromo-3,2'-bithiophene as a raw material, and carrying out t-BuLi double bromine lithium exchange and thiolizing reagent (PhSO2)2S ring closure to prepare the dithieno[2,3-b:2',3'-d]thiophene; or adopting 5,5'-bis(trimethylsilyl)-2,3'-dibromo-3,2'-bithiophene as a raw material, carrying out double bromine lithium exchange through n-BuLi, and thiolizing reagent (PhSO2)2S ring closure, and removing trimethylsilyl through trifluoroacetic acid to prepare the dithieno[2,3-b:2',3'-d]thiophene. The method 2 comprises: adopting 3-bromo-2,3'-bithiophene as a raw material, carrying out n-BuLi bromine lithium exchange while carrying out selective competition of protons, and carrying out thiolizing reagent (PhSO2)2S ring closure to prepare the dithieno[2,3-b:2',3'-d]thiophene; or adopting 3-bromo-5-(trimethylsilyl)-2,3'-bithiophene as a raw material, carrying out n-BuLi bromine lithium exchange while carrying out selective competition of protons, carrying out thiolizing reagent (PhSO2)2S ring closure and removing trimethylsilyl through trifluoroacetic acid to prepare the dithieno[2,3-b:2',3'-d]thiophene. According to the present invention, the synthesis process has operability, reaction conditions relate to no water, no oxygen and low temperature, and the method is suitable for laboratory scale preparation.