The corrosion behavior of 9Cr ferritic–martensitic heat-resistant steel was investigated in water and chloride environment at room temperature (RT). The results of linear polarization, electrochemical impedance spectroscopy (EIS), and potentiodynamics (PD) polarization tests on long-term exposure show that 9Cr ferritic–martensitic steel has weaker corrosion resistance and greater pitting corrosion tendency in higher chloride concentrations. Corresponding scanning electron microscopy (SEM) observation displays that higher concentration chloride promotes the pitting initiation. During long-term exposure, pitting susceptibility decreases, the average pit size increases, and the density declines in higher chloride concentrations. Pits in the grains and along the grain boundaries are observed by optical microscope (OM), and it indicates that inclusions in grains and carbide particles at grain boundaries are the sites susceptible to pitting initiation.