Electrochromic smart devices with tunable optical properties are on the verge of replacing the conventional windows and curtains. The preparation and commercialization of electrochromic materials are majorly based on vapor phase deposition which is limited by high price and difficult production processes. Here, atomizing spray deposition process is developed for the production of large area, low-cost electrochromic film. W18O49, a promising inorganic EC material, was used to prepare EC film on indium tin oxide-polyethylene terephthalate (ITO-PET) flexible substrate. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was also printed on ITO-PET substrate to improve the conductivity of substrate and the adhesion between W18O49 and substrate. The experimental results showed that the transmittance modulation (ΔT) of W18O49/PEDOT:PSS/ITO-PET flexible EC film was 63.34% corresponding to a wavelength of 633 nm. The coloring and bleaching response times of W18O49/PEDOT:PSS/ITO-PET EC film were 18.7 s and 23.2 s, respectively. Furthermore, the as-prepared flexible EC film by atomizing spray deposition method had excellent cyclic stability, and the optical transmittance of the film still retains a high value (70%) after continuous coloring and bleaching for 6000 s.