A theoretical model of the combustion of a nitramine solid propellant in the presence of a plasma jet is proposed. Unlike standard double-base compositions, nitramine propellants exhibit experimental evidence that plasma induces a burning rate enhancement. The model is based on heat transfer considerations and proposes a closed-form solution of the enhancement of the propellant burning rate as a function of the thermophysical parameters of the system. The model provides a good qualitative agreement with experimental results.