A new model is proposed for the analysis of fatigue crack growth under random loading. The fatigue rule of crack length is transformed into the monotony function rule based on types of the crack. By performing reliability analysis, the randomness of the stress, the stochastic nature of the crack growth, the fuzziness of the initial crack size and the randomness of the crack critical size are considered. The First-order-second-moment approximation method is used to obtain the solution of the probability density function. An example is given to illustrate feasibility of the proposed method.