Bubble flow has good characteristics of mass and heat transfer, and is widely used in industrial practice. In bubble flow, the gas phase is mixed with the liquid phase in the form of bubbles. The gas-liquid two-phase structure of bubble flow is investigated by analyzing the motion and force states of bubbles. The most crucial bubble behaviors include the bubble collision and breakup, which continuously occur in the movement process of bubble flow. The bubble collision is usually brought by the fluid turbulence, buoyancy and laminar shear stress. The coalescence efficiency of bubble collisions is analyzed to describe the bubble coalescence behavior. A novel theory of bubble breakup is established according to the probability field analyses of turbulent eddies. Then, the generation and elimination rates of an entire bubble group can be obtained by calculating the collision and breakup probabilities of a single bubble. Combing with the investigations on the random motion rules of a single bubble and an entire bubble group, a theoretical model is first developed to predict the overall bubble size distribution in fully developed bubble flow. The predictions from the probability model generally agree with the experimental data of the bubble size distribution, validating the applicability and easier usage of the theoretical model.