An innovative 3D flower-like BiOI/Bi3O4Br hierarchical heterostructures complex material was firstlyconstructed via in-situ growth of ultrathin BiOI on Bi3O4Br by a simple precipitation method. Underthe simulated solar-light illumination for 90 min, the optimal 60% BiOI/Bi3O4Br composite displayedthe highest photodegradation rate of 96.4% for RhB, 80.0% for TC and 77.2% for MO. The correspondingapparent rate constants were 0.0314, 0.0167 and 0.0110 min1, which were 8.26, 1.82 and 3.24-timesthan that of Bi3O4Br, 44.86, 11.13 and 2.62-times than that of BiOI. The improved photodegradation activitycould be owing to the following reasons: 1) The 3D hierarchical heterostructures endowed BiOI/Bi3O4Br with tight interfacial contact, which can supply sufficient migration channels for photoinducedcarriers; 2) The Z-scheme charge migrate pathway promoted the segregation of photocarriers whilemaintaining a robust redox ability; 3) The BiOI/Bi3O4Br heterostructures reinforced light absorptionedges more than 600 nm and augmented specific surface areas over 60 m2g1. In addition, the variousphotocatalytic conditions were studied to imitate the degradation process of RhB in the real aqueous system. The radical capture experiments and EPR test attested that h+ and O2played an important part inthe photodegradation of RhB.