Aimed warhead is an important tendency for air-defense missiles to enhance damage effect. The damage effect by which air-defense missile kills the target can be improved by regulating the optimal delay time of aimed warhead in different encounter conditions. In the article, the encounter model and the optimal denotation delay calculation model were built. The factor impacting the optimal denotation delay was analyzed. The simulation results demonstrate that the optimal denotation delay is not only related to encounter conditions, but also related to the servo system positions.