The issue of intercepting an incoming missile (attacker) with a certain intercept angle by a defensive missile (defender) launched from an unmanned combat air vehicle (UCAV) (target) is considered. Assuming the attacker adopts the augmented proportional navigation law and there is one way information transportation between the defender and the target, the nonlinear model describing the changing of the line of sight between the defender and the attacker is derived. With the consideration of the requirement of the defender’s miss distance, the constraint of defender’s terminal intercept angle and the control energy of the defender (or target), the performance index is established. The one way cooperative guidance law of the target and that of the defender, which can make the defender intercept the attacker with the designated intercept angle successfully, are deduced based on optimal control theory. Simulation results show that the defender can intercept the attacker with a designated intercept angle through the cooperative flight with the target under two kinds of oneway information transmission. The control energy under the one way cooperative guidance law of the defender is less compared with that under the non-cooperation guidance law.