On the problem of the interceptor guidance for air-based ballistic missile defense during the boost-phase, firstly, the time optimal control model is established, and the model constraints and controls is discussed combining the characters of the air-based ballistic missile defense task; secondly, the method for the interceptor feasible trajectory computing is put forward based on the Virtual arc; then the iterative computing method for trajectory-Shaping guidance law is designed based on the factors, viz. minimizing the interceptor flying time, minimizing the interceptor flying time distance and maximizing the confluence angle between the interceptor and the targeting ballistic missile at the hit point; lastly, the efficiency of the model and the arithmetic is validated by simulation.