In this paper the model of the propellant droplet evaporation with liquid phase dissociation reaction at high ambient pressure is developed，and the effect of polar gase compositions in combustion gases on the propellant droplet evaporation is taken into account. The characteristics of propellant droplet evaporation of the liquid phase dissociation reaction are analyzed by an example of the N₂O₄ liquid droplet evaporation. The calculation results show that this kind of propellant at high pressure evaporation does not obey the law of non-liquid phase dissociation reaction propellant. This model provides the new theoretical data and the calculation method for the analysis of the combustion process of the liquid rocket engine combustor.