Bismuth tetroxide（Bi₄O₇） was prepared by low temperature hydrothermal method using homemade potassium bismuth oxide（KBiO₃） as precursor and Bi₄O₇/BiOBr composite was successfully prepared by in-situ ion etching with hydrobromic acid.The phase and morphology characteristics of the samples were observed by x-ray diffraction（XRD） and scanning electron microscope（SEM）,respectively.The composite phase had better visible light degradation performance of Rhodamine B（RhB）than the single phase,which could reach 86.9% degradation in 30 min at most.Ultraviolet-visible diffuse reflectance spectroscopy（DRS） and Photoluminescence spectroscopy（PL） respectively proved that the improvement of the performance was due to the wider optical response range and lower photogenerated carrier recombination efficiency of the composite phase.·O ^2-and h ⁺ were the active substances in the photocatalytic degradation process of the system.According to this,a possible photocatalytic degradation mechanism was proposed.The composite phase had better photocatalytic degradation stability than the singlephase Bi₄O₇.