Determining the mechanism of transition from projectile‐impact ignition to detonation is a complex and difficult task with strong practical applications. Ignition due to low‐velocity projectile impact cannot be properly explained by the available theories. We attempted to determine the mechanisms of initiation of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX)‐based polymer‐bonded explosives (PBXs) in a range of high temperatures, which have rarely been investigated. Comparing the shock initiation results, we found that the low‐velocity projectile impact response mechanisms for a heated explosive are much more complex. Our results show that the impact ignition threshold velocity of the heated explosive does not always decrease with increasing temperature as commonly expected. A temperature dependent plastic power during impact controls the ignition in the range of 25 °C to 75 °C. At 190 °C and 200 °C, there was a sharp rise of reaction degree induced by β→δ phase transition for high HMX‐content PBX. Conversely, such phase transition effect becomes insignificant for low (<50 %) HMX‐content PBX. Our results show that three competing mechanisms affect the impact safety for a high HMX‐content PBX at high temperature, including plastic power, temperature sensitizing, and phase transition.