Abstract: From the viewpoint of force balance and fluxes, a general model of diffusion - reaction processes over a catalyst pellet for a non - ideal reaction system is developed. The thermodynamic characteristics of a non - ideal gaseous mixture and the interaction among the fluxes of different species are considered in the model. In addition, this model can be simplified to the conventional Ficks Model, Extended Stefan - Maxwell Model or Dusty - Gas Model. As the foundation for developing general software simulating the diffusion - reaction processes involved over a pellet of catalyst, this model has obvious advantage over others used usually.