Abstract: Methods, which are used to evaluate correlation parameters in fatigue multi-crack propagation random model using test data, were established. Taking advantage of the existed single-crack propagation test data, the parameter estimation method was established by using non-complete test data for analyzing the probability damage tolerance with multi-crack structure.Two cases (complete test data-far parallel crack and complete test data-near crack) were discussed to analyze the parameter estimation method as stated above by using least square method.At the same time, the extreme cases of crack propagation test were considered.Finally, a parameter estimation method whose estimation results inclined to conservative condition in the case of non-complete test data-near crack was developed.