In this paper, a series of Ag3PO4-BiOCl1-xBrx composites with adjustable band gap has been fabricated by using a facile two-step synthetic method. The photocatalytic activity of Ag3PO4-BiOCl1-xBrx was evaluated by photocatalytic decomposition of phenol aqueous solution under simulated solar light irradiation. The result shows that Ag3PO4-BiOCl0.75Br0.25 (1:5) composite possesses the best photocatalytic activity among all the as-prepared samples. The photocatalytic activity of Ag3PO4-BiOCl can be enhanced mainly owing to the strong light absorption ability by loading Ag3PO4 on the surface of BiOCl, while the photocatalytic activities of Ag3PO4BiOCl1-xBrx (x= 0.25, 0.5, 0.75 and 1) composites could be enhanced by restraining the recombination of photo-generated electron-hole pairs. The enhanced solar-light photocatalytic activities of Ag3PO4-BiOCl1-xBrx composites could be ascribed to the adjustable energy band structure, which facilitates the separation of photoinduced carriers. In addition, superoxide radicals (center dot O-2(-)),holes (h(+)) and center dot OH are considered to dominate the photocatalytic degration process. Moreover, a possible mechanism of deep understanding on the base of experimental results was proposed.