Abstract: The fatigue crack growth rate test was conducted on 300M steel in air atmosphere and 3.5wt% NaCl-water solution, and the fatigue crack growth rate-stress intensity factor range curves were obtained and fitted using Paris and Walker formulas, respectively. The effects of stress ratio, corrosion environment and frequency on the fatigue crack growth rate were analyzed. The results show that the fatigue crack growth rate of 300M steel increased with the increasing stress ratio; at the same stress ratio, the crack growth rate of 300M steel in NaCl-water solution was higher than that in air atmosphere during the early stage of crack growth, and tended to be the same in the later propagation stage; in the early stage of crack growth, the crack growth rate of 300M steel under relatively low frequency was higher than that under relatively high frequency.