Bi2O3/BiOI step-scheme heterojunction photocatalyst was synthesized with green calcination method and its degradation ability of tetracycline was investigated.The photocatalytic performance of the Bi2O3/BiOI heterojunction,Bi2O3 and BiOI was compared.The structure and morphology of the samples were characterized with X-ray diffraction (XRD),X-ray photoelectron spectrograph (XPS).The degradation rate of tetracycline was analyzed with spectrophotometry.The result of calculation showed that the degradation rate of tetracycline was 92.4% in two hours.The first order kinetic rate constant was 0.018 59 min-1.The result of calculation with density functional theory showed that the work function of Bi2O3 and BiOI was 3.0 eV and 6.0 eV,respectively.When this step-scheme heterojunction was used as a photocatalyst,the weaker electrons in the conduction band of BiOI were combined with the weaker holes in the Bi2O3 valence band under the combined effect with built-in electric field and band bending,retaining strong reducing and oxidizing ability of photoelectrons and holes,which may be the reason why Bi2O3/BiOI step-scheme heterojunction has higher photocatalytic activity.