Type II heterojunction TiO2-BiVO4 composite films were designed via modified sol-gel-hydrothermal method for solar photoelectrocatalysis (SPEC) to restrain the recombination of electrons and holes as well as expand light absorption range. Fiddlehead-shaped morphology resulted in a larger specific surface area (157.63 m(2).g(-1)) and an intensification of light-harvesting efficiency. In comparison with photocatalytic (PC) system (79.3%), the degradation efficiency of RhB increased significantly to 93.9% in SPEC system. The enhancement mechanism and degradation path of SPEC systems was further discussed based on energy band adjustment, main active group determination, and quantum chemical calculation. Furthermore, the acute ecotoxicity of RhB and its degradation products were tested by Vibrio fischeri. The ecotoxicity was almost completely eliminated in SPEC system but it increased in PC system. The nanocomposite film also represented an excellent recyclability and stability, which may greatly reduce the economic cost and limit the probability of secondary pollution. Therefore, TiO2-BiVO4 nanocomposite films exhibited great potential in SPEC, providing a sustainable and harmless technique to treat organic wastewater.