In order to study the effect of elastic stress and elastoplastic strain on the corrosion behavior of 921A steel in simulated seawater, the electrochemical properties of 921A steel under the synergistic action of load and corrosion, such as open circuit potential, potentiodynamic polarization curves and EIS(electrochemical impedance spectroscopy), were tested by a homemade load-electrochemical experimental device. The corrosion rate correction factor under stress was defined by the charge transfer resistance obtained by EIS, and the experimental corrosion rate correction factor was compared with the theoretical value. Results show that the effects of elastic tensile stress and the elastic compressive stress on the mechanochemical effect are symmetrical. The mechanochemical effect increases with the increase of the elastic stress, and increases first and then decreases with the increase of the elastoplastic strain. The effect of the elastoplastic strain on mechanochemical effect is far greater than that of the elastic stress. In the scope of this study, the maximum negative shift of corrosion potential caused by the elastoplastic strain is 62.6 mV, and the corresponding corrosion rate correction factor is 4.113, while those caused by the elastic stress are 24.5 mV and 1.746, respectively. Therefore, the effect of stress and strain on the corrosion behavior of 921A steel in seawater cannot be ignored.