Initial Discontinuity State is the characteristic of aluminum alloy, it is a random parameter. According to an advanced aluminum alloy rolling alclad sheet, the coupons were carried out tension and fatigue test, stress ratio R=0.06, 0.2, 0.5 and the maximum stress level σmax=403, 370, 330, 310, 280, 260, 240, 220MPa through Material Test System 810. By use of scanning electron microscope, the tension and fatigue fracture surface was analyzed and the flaw size was obtained. The metallographic coupons were prepared, the constituent particles were surveyed using KH-7700 optical microscope and particulate size was gained. Based on measuring data, different distributions (Normal, Lognormal, Weibull, Logistic, Gumbel) were verified, the best-fit distributions of tension and fatigue facture flaw size is Lognormal distribution, as same as that of θ phase. However, that of S phase size is Weibull distribution.