Coupling BiOCl nanoparticles (NPs) with BiOBr nanosheets is achieved by a facile alkaline hydrothermal method to obtain a high performance visible light driven photocatalyst. BiOBr nanosheets in the nanocomposite can absorb visible light to drive the photocatalytic process, and the BiOCl NPs are used to transfer the excited electrons out of BiOBr to form superoxide radicals. Due to the small size and uniform distribution of BiOCl NPs on BiOBr nanosheets, the hybrid nanosheets possess photocatalytic activity superior to that of pure BiOBr, and the typical photochemical reaction rate is two times that of BiOBr when BiOBr/BiOCl weight ratio is 10:1. The major reactive species during the photocatalysis are superoxide radicals as determined by trapping experiments. The coupling effects and the photocatalytic mechanism are also discussed based on the energy diagram analysis vis first principle based density functional theory (DFT) calculations and the photoelectric tests. The present BiOCl/BiOBr hybrid nanosheets provide new insights into the design and preparation of high-performance visible light driven BiOX (X = Cl, Br I)-based photocatalysts.