The effects of porous structure on the burning characteristics of foamed NC-based (nitrocellulose-based) gun propellants were investigated by closed vessel and quenched combustion experiments. The foamed NC-based TEGDN (triethylene glycol dinitrate) gun propellants with different porous structures were prepared by adjusting the process parameters in the foaming process. SEM (scanning electron microscopy) was used to observe the morphologies of foamed TEGDN propellants, and the densities of the foamed propellants were also measured to evaluate the porosities of foamed propellants. The experimental results showed that the burning characteristics of the novel foamed propellants are totally different from combustion characteristics of parallel-layer. Further investigations revealed that the burning characteristics of the foamed NC-based propellants largely depend on the porous structure, larger pores and higher porosity would lead to higher burning rate of the foamed TEGDN propellants.