The influence of sampling orientation, stress ratio and microstructures on the fatigue crack propagation behavior of 2050 aluminum alloy was investigated. The results show that the effects of sampling orientation and stress ratio on the crack propagation rates are quite significant in the near-threshold region and the stable-tearing crack growth region, while their effects are relatively small in the stable growth region. The fatigue crack growth rate in L-T orientation is the lowest, followed by the rate in T-L orientation, and the rate in S-L orientation is the largest. The effect of sampling orientation on the fatigue crack growth rate mainly depends on grain orientation, texture orientation and the orientation of second phase particle. The fatigue crack growth rate of stress ratio 0.5 is bigger than that of stress ratio 0.1, which are mainly related to the crack closure effect in the near-threshold region and remarkably influenced by the maximum stress intensity factor Kmax in the stable-tearing crack growth region.