The preparation and electrochromic properties of silica composite poly (3,4-dibromothiophene) photonic crystals (SiO₂@PDBrTh) were investigated. The modified Stber method was used to synthesise SiO₂ microspheres, then through the three electrode system to prepare SiO₂@PDBrTh composite photonic crystals. Under the parallel conditions, a pure PDBrTh film was prepared and used as comparison by using ITO glass as working electrode. The results show that when the ordered structure of photonic crystals is introduced into PDBrTh, the contrast is improved by 15.4%, and the coloring and fading response time are also accelerated. The color of the SiO₂@PDBrTh composite film changes from yellow-green to light blue, and the color difference is bigger than that of the pure PDBrTh film, indicating that the introduction of the ordered structure of photonic crystals into PDBrTh can improve its electrochromic properties and facilitate its application in smart windows, sensors and other fields.