To study the ignition mechanism of charge under the combined action of shock wave and fragment impact, the critical impact velocity of fragment corresponding to the ignition of impacted charge obtained by the experimental method of first compacting charge by shock wave and then impacting damaged charge by fragment was 446.9-449.4 m·s^-1. LS-DYNA program was used to numerically simulate the shock wave damage of charge based on the nodal constraint-separation method. Then, secondary simulation to the ignition reaction process of impact damaged charge under fragment impact was performed by full restart method. The critical impact velocity of fragment corresponding to the ignition of impact damaged charge obtained by “up-down” method is from 452 m·s^-1 to 453 m·s^-1, the experimental and numerical results are in good agreement. Results show that the nodal constraint-separation method and the full restart numerical simulation technology can be used to simulate the ignition of charge under the combined action of shock wave and fragments, the critical velocity of fragments impact ignition of charge damaged by shock wave is lower than that of non-damaged charge, and the damaged state of charge sensitizes the impact sensitivity of fragments. This reduces the critical velocity of fragment impact ignition.