The stress corrosion cracking behavior of two advanced high-strength steels (ultrafine bainite steel, Q&P steel) of the same composition in an artificial marine environment 3.5%NaCl solution was studied by means of microscopic characterization (SEM, XRD, EBSD), electrochemical test and slow strain rate stress corrosion test. The results show that being subjected to treatment with isothermal process,the aquired ultrafine bainitic steel presents significantly refined bainitic ferrite laths, companied with more thin film-like residual austenite herewith, presents higher strength and elongation at break. The bainite ferrite lath and residual austenite form a micro-electric couple, the lower potential of bainite ferrite acts as an anode thus suffered from dissolution, while the active dissolution site induces the initiation and propagation of cracks. In addition, ultrafine bainitic steel has fine grain, low stress during plastic deformation, thereby, lower stress corrosion sensitivity, which is due to the passivation of cracks caused by thin film residual austenite. Being subjected to treatment with quenching-partitioning process, the resulted Q&P steel presents thick and short martensitic lath with less amount of thin film residual austenite. However carbon in martensite is partially transferred to the residual austenite, nevertheless, the martensite and residual austenite also form a micro-electric couple, which significantly increases the electrochemical corrosion rate. The blocklike residual austenite in Q&P steel structure may be broken into brittle martensite under the action of stress, causing stress concentration leading to crack nucleation, dislocation accumulation and residual stress, which further promotes crack initiation and propagation.