The corrosion of steel reinforcement in underground engineering concrete, such as that found in coastal subways, is susceptible to occurring under the combined influences of stray current and corrosion ions. The corrosion behavior of steel reinforcement in different environments was studied. The real-time strain monitoring, electrochemical impedance spectroscopy (EIS), and microscopic analysis were employed for both ordinary Portland cement (OPC) concrete and alkali-activated slag (AAS) concrete. The results show that the steel reinforcement in concrete undergoes pitting corrosion. The chemical composition of corrosion products formed in the steel reinforcement appears to be unaffected by the type of concrete or the presence of corrosion ions. Furthermore, the corrosion rate observed in AAS concrete is found to be lower than that in OPC. Additionally, the time of deactivation of steel reinforcement and concrete rust expansion cracking is relatively logging behind. As the concentration of sulfate ions in saline soil increases, the rust cracking time and rust cracking force of steel reinforcement concrete increase first and then decrease. This suggests that sulfate ions have a mitigating effect on the corrosion rate of steel reinforcement induced by chloride salts.