Crack propagation tests are conducted on TA15 titanium alloy in three stress levels to investigate the stochastic characteristics of FCG. A random variable probability FCG model, base on the Paris’ law, is used to characterize the stochastic performance. Distribution significance test has been done, which shows that the random variable X can be considered reasonably to follow log-normal distribution in all the three stress levels. The probability distribution of crack size at any specified loading cycle and the probability distribution of the random fatigue life at which a given crack size is reached are discussed. Variance analysis indicates that the standard deviations of the log fatigue crack growth rate (FCGR) under the three stress levels do not differ from each other significantly. The scatter of crack initiation life under the lowest stress level is the largest, however, the scatter for crack propagation life shows no significant difference in the three stress levels.