The original bismuth-based oxyhalide, known as the Sillen family, is an important photocatalyst due to its high photocatalytic oxidation activity. Here, we report a bismuth-based photocatalyst, Bi24O31Br10, with reasonable reduction activity. The photoreduction capability of Bi24O31Br10 in H-2 evolution from water reduction is 133.9 mu mol after 40 h under visible light irradiation. Bi24O31Br10 presents the highest activity among Bi2O3, BiOBr, and Bi24O31Br10 in photocatalytic reduction of the Cr (VI) test, and Cr (VI) ions are totally removed in 40 mm. The Mott-Schottky test shows the bottom of the conduction band fits the electric potential requirements for splitting water to H-2. First-principles calculations indicate the conduction band of Bi24O31Br10 mainly consists of hybridized Bi 6p and Br 4s orbitals, which may contribute to the uplifting of the conduction band.