Fatigue damage plays a significant role in fatigue life of structures and mechanical parts. Characterizing crack length as a random process in fatigue life, is a matter of controversy which is the first step of this new stochastic model for prediction of fatigue crack propagation. Minimum uncertainties and capability of using closure load are the model advantages. Generating series of a nonstationary process, effects of load history in immediate last step of crack propagation using Total Probability Theory (TPT) are some assumptions of this model. The model results have been compared with actual test results of Ti-6Al-4V CT specimens.