Based on probabilistic fracture mechanics, the simulated durability test is performed to study the details with angle of side-frame of wagon bogie made of B grade steel. A new general computational method is proposed to evaluate the EIFS(equivalent initial flaw size) distribution, and the probabilistic crack exceedance model is established. The structural damage value is evaluated from the viewpoints of the survival probability P, stress level σ, crack initiation time t and economic maintenance limit a_e, and the corresponding economic life is predicted according to the actual measured stress spectrum. As a result, the TTCI(time to crack initiation) can be better characterized by the three-parameter Weibull distribution, and the validity of general EIFS distribution parameters obtained by the new computational method are verified by the K-S checkout. Furthermore, the structural damage value is quantitatively evaluated by the probabilistic crack exceedance model.The predicted economic life tends to increase with the increasing of the crack exceedance probability, and the rationality and validity of the new computational method and probabilistic model are proved.