In order to explore the vulnerability of Comp.B explosive at different temperatures and evaluate the effects of penetration depth and ambient temperature on the reaction level of Comp.B explosive, the armor-piercing incendiary of 12.7mm was used to penetrate Comp.B explosive at a speed of 850 m·s^-1. The response characteristics of Comp.B explosive at -40, 25, 70 ℃ were studied. The processes of bullet penetration were simulated by the non-linear finite element software ANSYS/LS-DYNA and the influences of mechanical properties of Comp.B explosives on vulnerability were investigated. Results show that the limit penetration depth of Comp.B explosive is 200~250 mm at 25 ℃. The highest level of response for Comp.B explosive at -40, 25 and 70 ℃ are deflagration, explosion and deflagration, respectively. The level of reaction of bullet penetration to Comp.B explosive is restrained at high temperature or low temperature. The decrease of shear modulus strength of Comp.B charges makes the degrees of response to Comp.B explosives reduce.