In order to explore the thermal safety characteristics of modified double base propellants， the thermal decomposition behaviors of modified double base propellants with RDX content of 0， 18%， 46% and 54.6% were studied by differential scanning calorimetry （DSC） respectively， and the thermal decomposition temperatures at different heating rates （2， 5， 10 and 20 ℃·min^-1）were obtained. The apparent activation energy， activation pre-exponential factor， reaction rate， Gibbs free energy， activation enthalpy and activation entropy were calculated by thermal reaction kinetics analysis， and the influence of RDX content on the double base components and apparent activation energy was also analyzed. The response characteristics of modified double base propellants with different RDX contents were obtained by slow cook-off and 5s burst point temperature tests. Results show that when RDX content is 18%， the apparent activation energy is the highest， and the response temperature and the response intensity of slow cook-off test and 5s burst point temperatures all are the lowest. The first decomposition peak temperature of samples moved backward， the apparent activation energy decreased， the slow cook-off response temperature moved to higher temperature， the thermal sensitivity of the system decreased， but the response level increased with the increase of RDX content. The response level is explosion， which could not pass the slow cook-off test when the RDX content is 46% or above. The 5s burst point temperature moves to high temperature with the increase of RDX content and presents a significant rising trend， and the thermal stability of modified double base propellants is improved.