The magnetic Fe3O4/BiOBr composites with different molar ratios were prepared by a new two-step method. The effect of different Fe3O4 contents on composites' properties was detected through XRD, SEM, TEM, HR-TEM, XPS, Uv-vis DRS, PL and BET. When the molar ratio of Fe3O4 nanospheres and BiOBr nanosheets is 0.5:1, the two are combined regularly to form 3D flower-like hierarchical heterostructure. This phenomenon is firstly found and can provide a reference for synthesizing other regularly combined magnetic heterostructure catalysts. The degradation activity for Rhodamine B (RhB) is much stronger than that of the previous studies under visible-light irradiation. 3D flower-like Fe3O4/BiOBr (0.5:1) heterostructure possesses great advantages including excellent magnetic separation, remarkable reutilization and stability. Through active species detection and liquid chromatography mass spectrometry (LC-MS) analysis, the degradation mechanisms of RhB are summarized (a) RhB photosensitization and (b) RhB moleculs attacked by radicals and a new possible degradation path was to be presented. This study offers a new method to prepare a regularly combined magnetic Fe3O4/BiOBr photocatalytic material and demonstrates its wonderful application for degradation of organic contaminants in aquatic environment. (C) 2019 Published by Elsevier Inc.