In recent years, nonprecious metallic Bi with the surface plasmon resonance (SPR) effect has attracted the attention of researchers in the field of photocatalysis and has been loaded onto the surface of various photocatalytic materials to study its effect on photocatalytic activity. In this work, the internal and surface of Bi₂WO₆ nanomaterials were modified by cleverly using the chelating and reducing properties of ethylene glycol (EG) to obtain photocatalytic materials with different metallic Bi modifications. A comprehensive analysis showed that modified Bi-BWO with a uniform distribution of metallic Bi was obtained by in situ etching on the surface of Bi₂WO₆ nanosheets, and the SPR effect of metallic Bi can be used to expand the light absorption range and improve the separation and migration efficiency of electrons and holes. Under simulated sunlight irradiation, the Bi-BWO sample achieved 100% degradation of a Rhodamine B (RhB) solution within 30 min, which was 25% higher than that of the unmodified sample. Bi⁰ inside the crystal structure caused lattice defects and served as a complex centre for photogenerated carriers, which decreased the photocatalytic efficiency. This study investigated the modification of different parts of photocatalytic materials with metallic Bi to introduce contrasting effects, developed a solution for in situ etching on the surface of modified bismuth-based photocatalytic materials, and provided a new idea to improve photocatalytic materials with cavities as the main active species.