Abstract: The paper reports the effect of0.01,0.1 and 1%NaNO2, a passive inhibitor, on corrosion fatigue (CF) crack initiation and propagation for a low strength structural steel A537 in 3.5%NaCl aqueous solution. The experimental results show that inhibitor increases the required cycles of CF crack initiation effectively, and this effect increases with increasing inhibitor concentration.However, there is nearly no effect of NaNO2 on CF crack propagation. The same CF crack propagation rate was found in all kinds of solutions. The results also indicate that the passive time in 1%NaNO2 solution during plastic deformation is much longer than cyclic time. NaNO2 passivates the specimen sudece and repairs passive film damaged by cyclic loading during the crack initiation. while the passsive film is not formed fully due to continuous plastic deformation at the crack tip during the CF crack propagation, which is much different from that in the stress corrosion cracking and general corrosion