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It is sparse and inconclusive that research on the subject whether the fatigue life of the structure will be reduced by shot peening strengthening before shot peen forming (S + F), and this study investigates accordingly. First, the crack growth rate test of the machine-processing plate and shot peening strengthening before shot peen forming plate demonstrate that both plates' final crack growth rate and length are similar. However, the test shows the "fluctuation phenomenon" of crack growth rate and the "intersection phenomenon" in the Paris curve. This study is based on a self-developed simulation plugin for crack growth paths. The results verify that "fluctuation" causes the differential distribution of the overall stress intensity factor in the strengthened (4.5% increase compared to machine-processing) and formed (9.8% decrease compared to machine-processing) crater areas of the shot peening strengthening before shot peen forming plate. Comparing to the full coverage strengthening area, the forming area (only 30% coverage) in the early stage of growth as well as the gain amplitude of the residual stress in the late stage of growth gradually decrease and tend to be the same as that of the machine-processing, as validated by the "intersection phenomenon". [ABSTRACT FROM AUTHOR]