TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): Compound (I) is prepared by taking compound (II) and compound (III) at mol ratio of 1:1.5-1.5:1, performing Stille coupling reaction at 50-120 degrees C for 6-100 hours in presence of solvent and catalyst under inert gas atmosphere, and separating and purifying. Compound (II) is prepared by dissolving 4,4'-dibromo-6,6'-diiodo-2,1,3-benzothiadiazole of formula (i) and chlorine-containing silicon compound of formula (ii) in N,N-dimethylformamide at mol ratio of 1:2 under inert gas atmosphere, slowly dropping n-butyllithium, cooling to - 78 degrees C, reacting while stirring for 2 hours, heating to room temperature, reacting for 10 hours, washing with water, extracting with ethanol, taking organic phase, drying with anhydrous sodium sulfate, filtering, vacuum-distilling and separating by silica gel chromatographic column. Compound (III) is prepared by dissolving brominated benzodifuran derivative of formula (iii) in tetrahydrofuran under inert gas atmosphere, cooling to - 78 degrees C, slowly adding n-butyllithium, reacting while stirring for 1.5-2 hours, adding tributyltin chloride, continuously reacting for 1 hour, heating to room temperature, reacting while stirring for 6 hours, adding saturated sodium chloride solution, stopping reaction, extracting with ethanol, drying with anhydrous sodium sulfate, rotationally evaporating to remove solvent and separating by neutral alumina chromatographic column. Preferred Components: The catalyst having adding amount of 0.5-20 mol is tris(dibenzylideneacetone)dipalladium, bis(triphenylphosphine)palladium dichloride and tetrakis(triphenyl phosphine) palladium. The solvent is tetrahydrofuran, dimethyl ether, diethyl ether, benzene or toluene. Preferred Method: Separating and purifying comprises extracting reaction system with toluene and deionized water, taking organic phase, vacuum-distilling to remove organic phase, precipitating with anhydrous ethanol, filtering, drying to obtain solid powder, dissolving in chloroform, passing in neutral aluminum oxide chromatographic column to remove organic solvent, settling, filtering, performing Soxhlet extraction with acetone for 3 days, settling and vacuum-filtering.