In order to study the relationship between the heating rate and the critical temperature of thermal initiation of cook-off bomb in defined conditions, experiments were carried out with a self-designed test setup. Cook-off bomb with RDX based high energy explosives was heated at a heating rate of 1 ℃·min^-1 and then makes the outer wall temperature of case keep at 160, 170, 180, 185 ℃ and 195 ℃ respectively for 50 min and then the response of cook-off bomb was observed. The critical temperature of thermal initiation of cook-off bomb at different heating rates was simulated by FLUENT software. Results show that explosive in constant high temperature environment is more dangerous than slow heating. The environment temperature of the reaction is lower and the response is more intense. When heating rate is 1 ℃·min^-1, the critical temperature of thermal initiation of cook-off bomb is 194.8 ℃. In addition, the critical temperature of thermal initiation increases slowly with the increasing of heating rate. When heating rate is larger than 10 ℃·min^-1, the critical temperature of thermal initiation is 197 ℃. When cook-off bomb is heated to its critical temperature of thermal initiation at different heating rates and then the temperature is kept constant until the response, the heating rate has no influence on the ignition position of cook-off bomb under the given conditions. Ignition point is always in the center of explosives.