Abstract Electrochromic smart devices with controllable optical property are the most promising alternative to traditional windows and curtains. State of the art preparation and commercialization of large-scale electrochromic films are mainly based on vapor phase deposition, but massive application is limited by high price (due to complex preparation process). Here, an all-solution technology is developed for large-area low-cost preparation of electrochromic films. A WO 3 /ITO dispersion was successfully developed; high electrical conductivity ITO nanoparticle networks along with ITO coating on glass can serve as extended 3-dimensional electrode, which can form microelectrical field and act as the pathways for electron diffusion to WO 3 nanorods. In fact, experiment results show that the surface resistance of WO 3 /ITO nanocomposite film decreased to 32% of the pure WO 3. In other words, the optimum WO 3 /ITO nanocomposite films in this study with "distributed conductive structure" and submicrometer-sized voids morphology have improved the electrochromic properties remarkably. Our optimized WO 3 /ITO films exhibit higher optical modulation than pristine WO 3 (ΔT = 81.7% vs 62.5% at 630 nm) and a faster switching speed (t b = 6 s vs 22 s). Graphical abstract fx1 Highlights • WO 3 /ITO films were prepared by a wet chemical wire-bar process at low-cost. • ITO networks form a "conductive particle bridge", which can serve as extended 3-dimensional electrode. • WO 3 /ITO nanocomposite films present outstanding electrochromic performance. [ABSTRACT FROM AUTHOR]