<p>The initial corrosion behavior of E690 steel in NaCl solutions with different chloride ion concentrations was studied using SEM, EBSD, electrochemical testing, and AFM. The results show that the microstructure of E690 steel is mainly composed of lath bainite. As the concentration of chloride ion increases, the corrosion potential of E690 steel becomes more negative, the corrosion current density increases significantly, and the corrosion resistance decreases. The corrosion resistance of steel is mainly controlled by the microstructure in the early stages of corrosion. The high dislocation density of bainite and the electrochemical activity of grain boundaries make it prone to corrosion. In low concentration NaCl solutions, corrosion mainly occurs at the grain boundaries of bainite laths. As the chloride ion concentration increases, the original `austenite grain boundaries exhibit obvious corrosion characteristics, which accelerates the corrosion rate.</p>