The paper studies the two-body coupling dynamics between the space platform and interceptor during launching process， as well as optimization of the impulse control of the interceptor. The space platform forms an orbiting relationship with the target satellite， keeping its launch tube axis aiming at the target satellite. After receiving the launch command， the interceptor shoots out from the launch tube. The Lagrange equation of the second type is used to establish the platform-interceptor two-body dynamics model. Due to the effect of the coupling of the two bodies， the attitude of the platform is perturbed， causing the interceptor unable to accurately aim at the target satellite while separating the tube. At the moment， a velocity impulse is applied to the interceptor through its small rocket engine to make the interceptor enter the intercepting orbit. While the interception is ensured， the impulse velocity is minimized to save fuel. The paper summarizes it as a nonlinear programming problem. A three-level optimization strategy is presented to solve it. Under the condition that the interception flight time is small compared with the period of the platform orbiting the target satellite， the average angular velocity of the orbiting flight can be regarded as a small parameter， and the canonical perturbation method can be used to obtain the first-order approximate solution of the nonlinear programming. Then the optimizing iteration process is started from the approximate solution as its initial guess value. Finally， a numerical simulation verification is carried out.