The characteristics of RDX (cyclotrimethylene trinitramine) based propellant combustion over a wide range of pressure (5–430 MPa or 49–4250 atm) were studied experimentally. The data obtained from a strand burner and a closed bomb system show the influence of RDX concentration, particle size, the addition of NGD (nitroguanidine) and different binders used on the burning rate characteristics. It was found that the use of very fine RDX powder (2–3 μm) and the addition of a small concentration of NGD help to eliminate the pressure exponent shifts. The thermal analysis of the RDX based propellants with a Perkin-Elmer Corp. Differential Scanning Calorimeter, Model DSC-2C, and SEM examinations of quenched propellant samples were conducted to study high pressure combustion mechanism of the nitramine propellants. The results revealed that the pressure exponent shifts of the RDX based propellants are related to the difference of decomposition of RDX and its binders, physical structure variation, burning surface change and chemical activation variation of N 2 O with pressure.