A mathematic model was developed in this paper to predict the two-phase flow distribution characteristics in a plate heat exchanger. The submodels of the pressure drops in both the channel and the distributor were established based on pressure balance equations. The submodels of both the phase split in distributor and the liquid film distribution in the inlet of distributor were established based on phase separation equations. The algorithm of the mathematical model was developed by interatively solving the pressure drop balance equations and the phase separation equations respectively. The predictions of the model were compared with the experimental data. The relative errors of pressure drop between mathematic model and experimental data are within ±20%. The relative errors of two-phase region height between mathematic model and experimental data are within ±13%.