Prediction of spray droplet diameter distribution depends on the various parameters such as physical properties, fluid velocity, and discharge environment and injector geometry. The stage of forming droplets has a great variety in size and therefore will be predictable with a statistical approach. The maximum entropy principle is one of the most popular and best ways to predict the spray droplet size distribution along with the conservation equations. Due to some drawbacks in this model, the predicted results do not match well with the experimental data. It is suggested to improve the available energy source in the MEP model equation by numerical solution of flow inside the injector based on the CFD technique. This will enhance the calculation accuracy of the turbulent kinetic energy of the output spray. In fact, by using this sub-model in the maximum entropy model, the prediction accuracy of the spray characteristics is improved. Also, the requirement of the maximum entropy model to the experimental data as inputs has been reduced. By the present coupled model, the effect of spray upstream on the droplet size distribution can be considered with a good accuracy. The results show a close agreement with the available experimental data.