Abstract: The fatigue crack growth threshold values and crack propagation rates of 2124 T851 Al alloy plate along TL and LT directions at different stress ratios were measured in experiments. The effective stress intensity factor ΔKeff, the threshold of effective stress intensity factor range ΔKeffth and the critical stress intensity factor K′C under cyclic loading were introduced into a full range fatigue crack propagation expression. The fatigue crack propagation behaviors of 2124 Al alloy along TL and LT directions at different stress ratios were predicted by the modified formula. The results show that the predicted results were in accordance with the experimental results, which means the modified full range fatigue crack propagation expression can be applied to describe the fatigue crack propagation rate of aluminum alloy 2124-T851 plate.