The combustion properties and thermal behaviors of energetic thermoplastic elastomer (ETPE) gun propellant and RGD7 nitramine gun propellant were studied by the closed bomb test, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The results show that in comparison with RGD7 nitramine gun propellant, the ETPE gun propellant has lower burning rate, longer burning time and the burning rate pressure exponent larger than 1, whereas the pressure exponent of RGD7 nitramine gun propellant is less than 1. For RGD7 nitramine gun propellant, the endothermic melting peak of RDX at 204.8 ℃ in the propellant is inconspicuous and the exothermic decomposition peak of RDX at 240 ℃ is lag behind the exothermic decomposition peak at 194 ℃ of the NC/NG, where as the thermal decomposition temperature at 263 ℃ of poly(BAMO/AMMO) in ETPE gun propellant is higher than the thermal decomposition temperature at 240 ℃ of RDX. The different combustion properties of two gun propellants are caused by the different thermal behaviour of main compounds in the propellants.