Firepower application is one of the core problem in anti-missile power construction, Firepower Planning of double-layer anti-missile combat in terminal phase is a Nondeterministic polynomial hard Modeling question. We analysis the problem, when to assign the interception missiles to the targets and give the model assumptions; Then we establish the direct interception missile assignment model in firepower planning of double-layer anti-missile combat This model break the research which targets only can be assigned to the weapon system or fire units in the past, assigned the interception missiles to ballistic missiles one by one, it's a new idea about firepower planning.