The effect of soaking temperature and stirring rate on the corrosion behavior of Q235 and Q345 steel in simulated seawater environment (3.5%NaCl) was investigated by using soaking experiment. The surface morphology and chemical composition of corrosion products were analyzed by means of SEM and EDS. The results show that the corrosion rate of Q235 and Q345 steel has little difference and increase with increasing temperature in static seawater environment, reaching approximately 0.28 mm/a at 40 ℃. The stirring rate has a significant effect on the corrosion behavior of Q235 and Q345 steel and the corrosion rate accelerates with increasing stirring rate. When stirring rate is 300 r/min, the corrosion rate reaches 1 mm/a that is about 3.5 times as big as temperature effect. Uniform corrosion was observed on Q235 steel in simulated seawater. But the local corrosion morphology is found on Q345 steel and the main corrosion product is iron oxides. The application of Q345 material should be cautious compared with Q235 material in the same seawater environment.