The influence of oxygen partial pressure on the microstructure, element distribution, and physical properties of Ag−Sn−In−Ni−Sb alloy after oxidation was investigated by thermodynamic calculation, XRD, OM, EPMA, and AFM. The results show that the higher the oxygen partial pressure is, the more fully the alloy is oxidized, the smaller the oxide particle size is, the more uniform the microstructure is, and the better the physical properties of the oxidized samples are. The relative density of the sample oxidized at 0.9 MPa is 98.3%, the conductivity is 60.2% (IACS), and the hardness is HV 130.1. The NiSbSn intermetallic compound in Ag−Sn−In−Ni−Sb alloy is oxidized to six different oxide configurations. In addition, the relationships among oxygen partial pressure, oxide particle size and physical properties were established, and the influencing mechanism of oxygen partial pressure on microstructure was also discussed.