The research in this paper presented a new modified logistic model which could satisfy the demand of data processing of nondestructive testing. Used least squares, adopted nonlinear regression, and applied Gauss - Newton iteration, by which introduced the detail estimation method of distribution parameter. The goodness of fit of the model was also evaluated by integrating a group of concrete reliability test data. Computational result indicates that prediction values of the proposed modified logistic model are in good agreement with the experimental results and the model is suitable for matching testing probability curve and has the higher prediction accuracy and better flexibility.