Abstract: To address the issues associated with conventional hydrothermal/solvothermal methods for synthesizing multimorphic BiOBr, such as long heating times, high temperatures, and the necessity to add additional modifiers or templating agents. In this work, a microwave-assisted hydro/solvothermal method was first employed to rapidly synthesize four distinct BiOBr morphologies (spherical (BiOBr_U1), flower-like (BiOBr_U2), thick-sheet (BiOBr_A1), and thin-sheet (BiOBr_A2)) within 2 hours, using only readily available ultrapure water and dilute acetic acid as solvents and modulating only the reaction temperature. Optical characterization demonstrated visible-light absorption capability for all BiOBr photocatalysts, with absorption edges around 440 nm; BiOBr_U1, BiOBr_U2 exhibited stronger absorption in the UV-Vis region. The photocatalytic degradation performance was evaluated using tetracycline (TC) and ciprofloxacin (CIP) antibiotics. Under visible light irradiation for 120 minutes, both BiOBr_U1 and BiOBr_U2 demonstrated favorable catalytic degradation activity. Notably, BiOBr_U1 achieved a degradation efficiency of approximately 76% for a 20 mg·L^–1 TC solution. Besides, the TC degradation still reached 51% after under through three cycling experiments. Furthermore, the band structures and work functions of the four BiOBr samples were elucidated through combined characterization analysis and DFT calculations. The valence band (VB) position of the sheet-like BiOBr was determined to be sufficiently positive to generate strongly oxidizing photogenerated holes (h⁺), reacting with –OH to produce primarily ·OH as the oxidizing active species. BiOBr_U1 microspheres possessed the highest oxidation and reduction potentials for their VB and conduction band (CB) positions, enabling the generation of both ·O₂⁻ via highly reductive photogenerated electrons (e⁻) and ·OH via photogenerated h⁺. This study provides a theoretical reference and technical support for the design and synthesis of BiOBr photocatalysts.