To research the operating characteristics of high-speed ramjet kinetic energy projectile during the process of self-ignition, the process of self-ignition of high-speed ramjet kinetic energy projectile based on the solid fuel of polyethylene was numerically simulated. The ignition delay time in the self-ignition, the change law of flow field in combustor before the blanking cap opening, and the change law of flow field and performance of the entire ramjet after the flame in combustor stabilizing when the blanking cap opening were analyzed. Results show that because of its initial unique structure whose exit of nozzle is blocking, the ignition delay time is short enough, so the self-ignition can be successfully performed. Violent oscillation of pressure is occurred in the combustion chamber before the blanking cap opening, and chemical reaction in the combustion chamber enhances the effects of oscillation. After the blanking cap opening and flame in combustor stabilizing, the high-speed ramjet kinetic energy projectile′s rated thrust is 283 N and its net thrust is 83 N. The specific impulse based on polyethylene is 9129 m·s^-1.