Bi-doped Ag3PO4 was synthesized by an ion exchange method, and its structure and properties were characterized systematically. Doping Bi3+ ions into the crystal lattice of Ag3PO4 changed the properties of particles, reduced the valence band position and widened the band gap of Ag3PO4. The doped Bi3+ ions have replaced P5+ ions of P–O tetrahedrons according to the XRD and XPS analysis. The testing of methyl orange (MO) photodegradation showed that 2wt% Bi-doped Ag3PO4 had the highest activity, with the degradation rate reaching 90.7% after 6min (1g/L catalyst) when pure Ag3PO4 degraded only 27.3% of MO. Its degradation rate constant was 4.5 times that of undoped Ag3PO4. Particularly, 2wt% Bi-doped Ag3PO4 managed to photodegrade high-concentration (40mg/L) MO (1g/L catalyst), with the degradation rate constant 7.3 times that of undoped Ag3PO4. •OH radicals were the main active species in the oxidation of MO over Bi-doped Ag3PO4. Doping Bi3+ substantially reduced OH defects on the surface of Ag3PO4, which significantly increased the degradation efficiency of MO over Ag3PO4. In addition, the density-functional theory calculation revealed that the influence of Bi dopants on the electronic structure may be an important reason for the enhanced photocatalytic performance of Ag3PO4.