Abstract: In nuclear power plants, the flow accelerated corrosion (FAC) of carbon steel occurs mainly in the secondary circuit, causing a significant impact on production safety. According to engineering experience and experiment data, carbon steel pipes with Cr more than 0.1% can greatly reduce or avoid the FAC, and based on the high cost performance, SA335-P11 steel with Cr greater than 1% is recommended for steam pipes of nuclear power plants. In order to confirm the P11 steel surface oxide film under wet steam at high velocity, the small tubular specimens to finish FAC experiments were adopted, achieving the sample weight loss and morphology of inner surface corrosion. Experimental results show that a clear FAC morphology is formed at the inlet part of sample and the surface oxide film is damaged severely, and in the center of the sample, flow accelerated corrosion is not obvious. CFD simulation results show that the entrance velocity is about 24% higher than the average flow velocity, resulting into larger surface shear force, which is consistent with the experimental results.