To find out the influence of oxygen concentration on reinforcement corrosion in seawater sea-sand mortar, the wire beam electrode (WBE) technique was introduced. The influences of oxygen concentration (5%, 21%, 85%, volume fraction) and water-binder ratio (W/B) (0.48, 0.18) on time-dependent behavior of corrosion potential and electrochemical impedance spectroscopy (EIS) of WBE were separately investigated. Results show that the polarization resistance of WBE decreases and corrosion current density increases with the increase of corrosion time. The changes are greater with the increase of oxygen concentration and W/B.It can be observed from the experimental results that the corrosion probability of reinforcement increases with the increase of oxygen concentration. At a low oxygen concentration (5%), the reinforcement depassivation induced by chloride can be effectively retarded and thus the reinforcement corrosion is restrained. While at a high oxygen concentration, the reinforcement experiences a nonuniform corrosion process with progressive oxygenation from part to the whole. The anticorrosion capacity of reinforcement in seawater sea-sand cement-based systems can be effectively improved by decreasing W/B.