Abstract: At present, the theoretical study of liquid-liquid two-phase flow mostly focuses on the macro-kinetics behaviors of liquid drop swarms in the reactors while the microscopic mechanisms of drop-drop interaction are not researched thoroughly. In order to investigate, the interaction between two collinear rising liquid drops (oil drops) of oil-water two-phase flow, based on the theory of liquid-liquid two-phase flow, the oil-drop motion model was established by using the phase field method of Cahn-Hilliard equation in the simulation software COMSOL. By virtue of this model, the influences of drop-drop distance, drop size and two-phase physical parameters on the drop-drop interaction were simulated and the effects of the wake between drops on the drop coalescence were analyzed. It is indicated that leading drop's wake affects the floating velocity of its following drop, promoting the coalescence of two drops. And the larger the drop-drop distance is, the weaker the effect is. And the larger the drop size is and the lower the viscosity is, the shorter the coalescence time is. The research results provide the reference for the further study of more complex liquid-liquid two-phase flow systems.