Abstract: The SCC (stress corrosion cracking) susceptibility of steel l6Mn in nitrate solution was studied. The results showed that applied potential polarization would accelerate(anodic polarization) or retard (cathodic polarization) the SCC process. The study on phase electrochemistry revealed that there was significant difference in electrochemical performance between ferrite and pearlite of steel 16Mn. Pearlite preferentially corroded under the action of galvanic cell. The observation on time and in situ showed that corrosion started first at the phaseboundary between ferrite and pearlite, and the pearlite gradually corroded until disappeared, and then corrosion crossed the phase boundary extending into the ferrite phase. According to this, an anodic dissolution mechanism of SCC was proposed, on which pre-existing sting active path and phase electrochemistry (PEAP-PEC) jointly came into action (SCC mechanism of PEAP-PEC).