The thermal stress fracture of polymer bonded explosive （PBX） was studied by a combined simulated and experimental method using notched PBX cylinders. A 2D axisymmetric finite element model， which contained temperature related material properties， was employed to calculate the thermal elastic-plastic response of PBX cylinders under the condition of the initial cooling temperature of 50 ℃ and cooling rate of 10 ℃·min^-1. Temperature， strain and acoustic emission （AE） measurements were used in an air-cooling test for verification. Simulation results show that there is a temperature boundary layer near the surface and a temperature difference in the cylinder， resulting in tension stress greater than the strength of the PBX. A circular notch in the cylindrical surface distinctly amplifies the thermal stress and the stress gradient. The factor of stress concentration reaches a maximum of 1.6 when the notch radius is 2 mm. The PBX endures brittle broken during thermal shock when thermal stress exceeded its tension strength， accompanied with strong AE signals and a sharply decline on strain-time response. The critical fracture temperature of cylinders with and without a notch determined by simulation are respectively 8.3 ℃ and 12.6 ℃， while the value determined by experiment are respectively 9.2 ℃ and 12.5 ℃.