Biodegradation process especially at the interface of bioabsorbable metals is difficult to track using conventional analysis strategies (e.g. weightloss measurement and ex-situ surface characterizations). However, assisted by advanced spatially resolved localized techniques, the underlying complicated degradation mechanism emerges in sight. The evolution of local pH and O₂ concentration at the interface of biodegrading metals discloses the progression of the degradation products, particularly the precipitation of Ca-P-containing products, which occupy a significant role during metal biodegradation. In this work, a comparative local measurement of pH and O₂ concentration was executed at the interface of Mg, Zn and Fe alloys in Hank’s balanced salt solution (HBSS) at 37 °C under hydrodynamic conditions. The results revealed that the formation of Ca-P-containing products controlled local pH at the metal interface, and prevented the metal substrate from the interaction with oxygen and water. Local pH at the interface of Mg alloys in Ca²⁺-containing HBSS was found low and stable (7.5-8.1), demonstrating a slight alkalization on degrading Mg in the quasi-physiological environment. A strong consumption of oxygen was found on degrading Zn and Fe, indicating a potential oxygen deficit around Zn- and Fe-based implants. These findings provided valuable insights into the degradation mechanism of bioabsorbable metals.