Bismuth oxide (Bi2O3) is an important visible-light-driven photocatalyst, which possesses an application potential in photocatalytic degradation of organic pollutants and treatment of wastewater. However, low specific surface area and rapid recombination of carriers lead to a poor photocatalytic performance of Bi2O3, seriously restricting its application. Besides, the particle morphology of Bi2O3 is also not conducive to recycling and application. In this work, a flexible Bi2O3/carbon paper composite photocatalyst was prepared via electrochemical deposition and subsequent in-situ oxidation to improve its photocatalytic performance and operation convenience. In the as-prepared composite photocatalysts, fern-like β-Bi2O3 with a hierarchical structure is grown on the carbon paper substrate. In the visible-light-driven photocatalytic degradation of phenol in water, the photocatalytic performance of Bi2O3/carbon paper composite can surpasses α-Bi2O3 powder without a hierarchical structure and precedes the β-Bi2O3 with a hierarchical structure. Based on the analysis of N2 adsorption, diffuse reflection spectra, photoluminescence and reactive radical, the improved activity of Bi2O3/carbon paper composite is ascribed to the fern-like hierarchical structure of Bi2O3 and the electron capturing role of conductive carbon paper. The hierarchical structure favors the light absorption of Bi2O3 and its contact with reactants, while the electron capturing role of carbon paper can effectively separate the photogenerated electrons and holes in Bi2O3, thus promoting the utilization of carriers. In addition, the macro-size, flexibility and two-dimensional morphology of the composite also make the operation and recycling more convenient. This study provides an effective strategy for the design of flexible photocatalysts with a hierarchical structure.