The effects of density of grain-molded gun propellant and surface treatment of based-propellant on combustion performance of the grain-molded gun propellant were studied by closed-bomb test and 30 mm simulation ballistic gun test using high energy grain nitramine propellant RGD7A-6/7 as based-propellant. The characteristics of p-t and L-B curves for grain-molded gun propellant with different modular densities and different surface treatment of based-propellant were analyzed. The influences of density and surface treatment on the combustion property of the grain-molded gun propellant were obtained. The results show that in the density range from 1.0 g·cm^-3 to 1.5 g·cm^-3, the higher the density of the grain-molded propellant is, the better its progressivity is. The progressivity of grain-molded gun propellant MD7 obtained with surface-deterred and then surface-coated for based-propellant is the best. The muzzle velocity of MD7 at chamber pressure of 29.7 MPa increases by 6.6%. The muzzle kinetic energy increases by 13.8%.