The impact crack-closure retrofit (ICR) treatment was applied to cracked specimens. Two fatigue test stages were applied: the first stage was designed to prefabricate the fatigue crack, and the second stage was used to evaluate the retrofitting effect by assessing fatigue life. The stress was monitored through strain gauges during the fatigue test, and the stress intensity factor (SIF) at the crack tip was determined by a two-strain-gage technique. The extended finite element method (XFEM) was adopted as a means of acquiring the stress in each specimen, or the SIF, where it is difficult to measure it during the fatigue test. The test results show significant improvement on the delay of crack propagation due to the ICR treatment, as well as the fatigue resistance within cracked areas. Moreover, the cracked section is enhanced when closing the crack surface through the comparison of the stress variation with, and without, crack closure. The SIF at the crack tip decreased by about 36%, slowing down the crack growth rate, according to the fracture mechanics due to the change of crack profile and stress redistribution.