Indium tin oxide (ITO) electrode was modified with triethyoxy-2-thienylsilane (TETS), and then the polythiothene (PT) film covalently bonded to ITO electrode (PT-ITO) was prepared by the electrochemical polymerization. It was found that the adsorption force of PT on ITO electrode was enhanced, PT-ITO exhibited better stability. Cyclic voltammetry (CV) and UV-vis spectroscopy measurements indicated that the doping/dedoping reproducibility of PT-ITO in electrolyte was good. When the applied potential was 0 V, PT-ITO exhibited red color. While the positive potential was higher enough, PT-ITO exhibited grey-blue color, and the color change of PT-ITO was reversible. Moreover, PT film on ITO substrate chemically modified with TETS (T-ITO) was used to successfully fabricate an electrochromic (EC) device that exhibited stable EC switching as a function of applied potential. This again demonstrated that chemical bonding approach could bring about stronger interactions between the PT and ITO substrate, improving the EC properties.