A typical unsteady internal ballistic analysis model was proposed to take account of the erosive burning with the variance of local velocity and pressure along the grain surface of a solid rocket combustor. To validate the model of concern in the study, both cases of non-erosive and erosive burning were compared with the previous researches with marginal accuracy. It was quantitatively investigated that the combustion pressure, grain length, initial temperature, and vaporization temperature of propellant affect the erosive burning characteristics.