Interception probability is an important index to evaluate the effectiveness of anti - missile operations, and is critical to pre-war mission planning. Select an interceptor to establish its reachable area in the space, for the situation of midcourse anti-missile in the retrograde rail to intercept , determine its kill area in space. For any case where the kill area may be an intercept point, for a trajectory of a incoming missile, select the theoretical interceptor on the arc to intercept. So as to obtain the intercept point in the killing area of different height, different distance and at different intersection angle on the impact of the probability of intercept by selecting different height on the theoretical intercept point and adjusting the launch of the interceptor position. It provides a reference for the deployment and tactics of the deployment of anti-missile operations.