Aiming at the fatigue fracture problem of light Al-Li alloy in service environment, the third generation aluminum-lithium alloy 2195-T8 was taken as the research object. Experimental and simulation of the fatigue crack propagation behavior of the third-generation 2195-T8 Al-Li alloy with defects was investigated by constant amplitude tensile fatigue test and equivalent crack model. The results show that the fatigue crack starts at the bottom of the defect, and the crack growth rate is the fastest in the surface length direction, but the slowest in the depth direction. The fatigue fracture of 2195-T8 aluminum-lithium alloy has a typical delamination phenomenon, and the delamination of alloy greatly hinds the crack tip depth direction expansion, resulting in crack bifurcation. After the crack bifurcation, the propagation rate increases sharply, and the plastic region volume at the tip increases rapidly, which makes the alloy enter the rapid fracture zone. The above results show that the fatigue life of 2195-T8 Al-Li alloy with defects is reduced by crack propagation inclination and delamination.