Abstract: The effect of electrode potential on stress corrosion cracking (SCC) behavior of 321-52M-690 dissimilar weld joint in pressurized water reactor (PWR) was investigated by slow strain rate tensile (SSRT) tests and high-temperature electrochemical test in 300 ℃ water containing 50 ppm chloride. The results show that the SCC susceptibility increases with the electrode potential (-700-+100 mV), and a critical potential E_crit between 0-+50 mV (vs. SHE) exists. The SCC susceptibility is low, and no obvious intergranular or transgranular stress corrosion cracks can be found when the electrode potential is below E_crit corresponding to deoxygenated water chemistry. While, when the electrode potential is more positive than E_crit, dramatically, I_SSRT is above 70%, and all the brittle fractures locate at 321 base metal, where exhibits significant SCC behavior with large area intergranular and transgranular stress corrosion cracks. The 321 base metal is the most vulnerable to SCC in this dissimilar weld joint, so the stress corrosion cracking mechanism of 321 stainless steel was further discussed in this paper.