The phase transition behavior of HMX-based polymer-bonded explosives （PBX） and pure HMX pellet， prepared by compression molding， was studied by variable temperature wide-angle X-ray scattering （WAXS） and differential scanning calorimetry （DSC）. The HMX-based PBX contained polyester polyurethane （HMX-Estane）， fluororubber （HMX-F₂₃₁₄）， as well as nitrocellulose （HMX-F₂₃₁₄-NC）. The initial β→δ phase transition temperatures （T_i）， as determined by WAXS， were found to be 186 ℃ for HMX-Estane（95∶5）， 188 ℃ for HMX pellet， 192 ℃ for HMX-F₂₃₁₄（95∶5）， and 198 ℃ for HMX-F₂₃₁₄-NC（95∶3∶2）. The addition of the small amount of nitrocellulose （2%） to the binder increased the T_i by about 10 ℃， compared with HMX pellet. All samples retained the δ-phase when cooled from the high temperature phase to 100 ℃ and kept in vacuum for 12 h， except HMX-Estane which went through a reversible phase transition and changed β phase completely after kept at 100 ℃ for 3.5 h. Among the three types of binders only Estane promoted the β→δ phase transition and the reversed δ→β transition of HMX. This result was attributed to the dissolution （on heating） and the precipitation （on cooling） of β-HMX at the HMX-Estane interface.