We establish a facile strategy by solvothermal reaction and hydrogenation to synthesize 2D WO3 ultrathin nanosheets with abundant oxygen vacancies. We find that the hydrogenated WO3 ultrathin nanosheets exhibit outstanding electrochromism properties. Moreover, the hydrogenated WO3 nanosheets also exhibit remarkable photocatalytic performance. The outstanding electrochromism and photoelectrochemical performances are mainly due to increased oxygen vacancies and narrowed band gap.