The characteristics of fatigue crack propagation behavior under constant cyclic load and cyclic load including tensile overload have been compared in the thermomechanically treated Al 7039 alloy and the peak aged. Crack closure mechanism owing to surface roughness is found to be related with the higher fatigue resistance in the peak aged condition under constant load. During overload crack branching, in addition to residual stress induced crack closure, was observed to be an another important mechanism for the retardation of fatigue crack growth rate following overload. More significant crack branching observed in thermomechanically treated condition is intimately related with the higher retardation of fatigue crack growth. The primary mechanism of fatigue crack growth retardation due to overload varies with the loading condition and microstructures. Consecuently the retardation of fatigue crack growth becomes more obvious in lower stress intensity factor range and higher overload ratio.