A simplified mechanism of the plasma effect on the combustion on different types of propellants is presented. The model provides a semi-quantitative prediction of the burning rate enhancement that should be expected for a given propellant composition and structure. Depending on the propellant structure and composition, one expects a burning rate enhancement either to disappear or to survive a certain time after the plasma injection has been turned off. In order to estimate the internal front propagation rate, we have built a simplified model of the RDX ignition inside the matrix. A cubic lattice topology has been assumed and the ignition front extends from one layer to its nearest neighbor. The propagation rate was found to be dependent on the lattice constant, the particle size, the thermo-chemical properties of the RDX particles and the matrix background.