A tungsten oxide thin film (WO_x) with 30% oxygen content was sputtered on indium tin oxide (ITO) glass by DC reactive magnetron sputtering. On this basis, tantalum oxide thin films (TaO_x) with different oxygen content were sputtered. The phase structure and the relative change of elements of tantalum oxide film were analyzed by X-ray diffraction and energy dispersive spectrometer. The surface morphology of tantalum oxide film was analyzed by scanning electron microscopy. The transmission of tantalum oxide film was measured by ultraviolet spectrophotometer and electrochemical workstation. The electrochromic property of tantalum oxide film was studied. The results show that the sputtering tantalum oxide films are all amorphous structure. With the increase of the oxygen content, the oxygen content of the films is close to 71.4%, and the protection performance of the films to tungsten oxide shows a downward trend. When the oxygen content is 70.08%, the optimal protection performance to tungsten oxide is obtained. At this time, the coloring response time of the electrochromic films is 21 s. The addition of tantalum oxide film reduces the switching peak current and leakage current of the electrochromic film, and keeps the charge capacity stable and improves the cycle stability of the device.