Abstract: Fatigue crack growth rates of ST12 low carbon steel plate under different stress ratios (R=0.2, -0.3,-1) were tested, the crack growth rate curve characterized by the effective stress intensity factor range was obtained by Newman crack closure model. The results show that the crack growth rate of ST12 low carbon steel plate under different stress ratios increased with the crack length. When the stress intensity factor range was constant, the crack growth rate increased with the stress ratio. The stress intensity factor range at fracture of ST12 low carbon steel decreased with increasing stress ratio. The crack growth curves under different stress ratios agreed well with each other when characterized by the effective stress intensity factor range, and the crack closure was the main reason for the difference in crack growth rates under different stress ratios.