Due to the advantages of small volume, light weight and flexibility, flexible electrochromic (EC) devices have drawn much attention in various fields, such as flexible display screens, smart windows, information storage, electronic paper and energy-saving bracelets, etc. EC materials can be classified into two categories: inorganic and organic systems. Compared with organic EC materials, inorganic EC materials display good stability and reliability. Prussian blue and transition metal oxides are the two major classes of inorganic EC materials. Up to now, most reported EC devices in literatures are deposited on rigid substrates. It is still a major challenge to realize excellent EC devices on flexible substrates. Combining EC materials with flexible substrates is expected to have great application prospects in future smart clothes and implantable displays. In this work, potassium ferricyanide, potassium chloride and anhydrous ferric chloride were used as precursor. Prussian blue (PB) was deposited on ITO-PET flexible substrate by electrodeposition method to prepare PB/ITO-PET EC film. Scanning electron microscope, ultraviolet spectrometer and electrochemical workstation were used to characterize its microstructure and electrochemical performance. The experimental results showed that the light absorption rate of PB/ITO-PET EC film with the electrodeposition time of 200 s was 0.755 at the wavelength (λ) of 700 nm. The PB/ITO-PET EC film was colored and faded at low voltage (0.6 V/-0.3 V). The light modulation range, coloring/fading response time, coloring efficiency were 68%, 9 s/8 s and 108 cm2/C, respectively. The light modulation range and coloring efficiency of PB/ITO-PET EC film after 1000 coloring-fading cycles were 68% and 100.3 cm2/C. The coloring efficiency was 105.5 cm2/C after 500 bending, and the coloring efficiency and light modulation range of PB/ITO-PET electrochromic film were 91 cm2/C and 65% after 500 bending and 1000 coloring-fading cycles. Finally, a flexible EC device was assembled using ITO-PET as ion storage layer (counter electrode), gel electrolyte and PB/ITO-PET as working electrode, and its light modulation range and coloring/fading response time were 53% and 13 s/18 s, respectively.