The phase distributions and mechanical properties of annular flow are constantly fluctuating, so they can be regarded as random states. The probability analysis of annular flow is an appropriate method to research the formation, development and evolution of the flow pattern. In the present work, the atomization and deposition rates of fully developed annular flow are investigated in detail by the method of a probability analysis. First, the basic equations of the probability model are applied to solve some important intermediate parameters of annular flow. Second, the atomization and deposition rates of any size droplets are closely related to the probabilities of droplet generation and disappearance. Third, the interchange rate of the whole liquid phase can be obtained by summing the generation and disappearance probabilities of arbitrary size droplets. The predictions of atomization rate are well verified by comparing with the experimental date of 71 cases from three sets of tests. It is demonstrated that the probability model can accurately calculate the atomization rate of the fully developed annular flow for most cases. The predicted deviation for some cases may be caused by the neglect of droplet breakup process. Furthermore, the effects on the atomization rate of seven parameters of annular flow are discussed in detail.