In order to obtain the thermal cycling properties of octogen（HMX） and triaminotrinitrobenzene（TATB） based polymer bonded explosive （PBX） ， the thermal cycling tests of HMX- and TATB-based PBX were carried out under the condition of -40—75 ℃. P-wave and S-wave velocity of explosive specimens with 3N （N=0，1，2，…，9） cycles were measured by ultrasonic echo method. The dynamic elastic modulus （Young"s modulus， shear modulus） and dynamic Poisson"s ratio were calculated by ultrasonic measurement method. The static elastic modulus was measured directly through the tensile property test， while the ratio of dynamic and static elastic modulus was calculated. Results show that the density of HMX-based PBX decreases and later the decrease rate slows down with the increase of the cycle number during the thermal cycling test. The density of TATB-based PBX decreases first， then the decrease rate slows down， and finally has a slight upward trend. The change trend of P-wave velocity， S-wave velocity and dynamic elastic modulus of HMX- and TATB-based PBX are consistent with the change trend of their density respectively. Their corresponding dynamic Poisson"s ratio is basically unchanged. There is a positive linear relationship between P-wave ， S-wave velocity and its density. The static elastic modulus first decreases and then increases， the dynamic and static elastic modulus first increases and then decreases， where the inflexion point of HMX-based PBX is in its 15st thermal cycle， and that of TATB-based PBX is in its 21st thermal cycle. The results show that the damage quantity of PBX during thermal cycling is closely related to its density change and internal micro damage. All these phenomenon demonstrate that the ultrasonic longitudinal and shear wave velocities can be used to quantitatively evaluate the thermal fatigue damage of PBX in thermal cycling test. The change trend of the dynamic and static elastic modulus of PBX is related to its micro structure evolution including internal micro-cracks and binder flow in micro-pores.