Thermal decomposition of three modified double-base propellants and their major component RDX were investigated by using high pressure differential scanning calorimeter(DSC).The change of the decomposition peak temperature,the peak tempertures difference,the apparent enthalpy and the curves of decomposition at different pressures were observed. The influence of pressure and the burning catalyst on the process of thermal decomposition were discussed and tentatively correlated with the burning rate and the pressure exponent of burning rate.