The work aims to improve the performance of the electrolyte by polyethylene glycol 400 and dissolve the UV-cured resin in the electrolyte to prepare all solid state electrolyte by UV cure in view of that WO3 electrochromic thin films prepared by sol-gel rotary coating have many cracks on the surface and long cycle response time after annealing and encapsulation with liquid electrolyte has the disadvantages of difficult operation and easy leakage. WO3 thin films doped with polyethylene glycol 400 were prepared by sol-gel method. The gelatinous electrolyte was prepared with lithium perchlorate powder, polycarbonate, polymethyl methacrylate powder and UV-cured resin. The WO3 thin films were sealed and cured by capillary encapsulation. The response time, light transmittance and memory effect of the prepared electrochromic device were tested, and the surface morphology of the film was analyzed with scanning electron microscope. The surface cracks of WO3 thin films doped with polyethylene glycol 400 were obviously reduced, and the average roughness was 3 nm with more loose pores. It only took 0.5 s to achieve the complete coloring effect of the undoped group for the prepared electrochromic device, while the complete coloring of electrochromic devices made by not doping PEG400 required 4 s. It took 0.5 s for the electrochromic devices prepared by doping PEG400 to fade, while the complete fading of electrochromic devices made by not doping PEG400 required 1.5 s. The optical modulation amplitude of the doping group was 20% higher than that of the undoped group, and the memory effect was also better. Doping PEG400 can make the surface of WO3 thin films more uniform, effectively increase the optical modulation amplitude and reduce the cyclic response time, and the memory effect is also obviously improved. At the same time, the preparation of all-solid-state electrochromic devices by UV curing technology is simple and easy to save.