Abstract: In order to study the mechanism of overload retardation effect, it is necessary to know the stress and strain distribution in the intense strain region at the crack tip under elasticplastic conditions. It has been proposed that at the crack tip exists a process zone in which the micro-fracture process takes place. However, the experimental verification has not appeared.By using the recrystallization technique, the large plastic strain in the ' intense strain region at the crack tip has been measured for compact tension specimens when an overload was applied to them under constant amplitude cycling loads. The parameters in this region and the J-integral has been determined, and the retardation effect of the crack tip opening displace-ment（CTOD） and the overload on the fatigue crack growth has been found. The experiment results show that the recrystallization technique is a very useful method for evaluating the retardation effect of an overload on crack growth.