With the development of unmanned military technology， unmanned short-range air combat has attracted much attention from military powers in the world. Faced with the threat of high-speed and high-maneuverability attacker missiles， traditional passive defense measures such as throwing chaffs or releasing hot flame bombs fail to ensure the safe escape of target aircraft. It is a feasible method to implement active defense by launching defender missiles to coordinate the maneuvering of target aircraft. However， due to the strong maneuverability of the attacker missile and unknown acceleration information， it is difficult to design the guidance law of cooperative target aircraft-missile. An active defense line-of-sight （LOS） guidance law based on disturbance compensation was proposed in this paper. A nonlinear disturbance observer was designed to estimate the influence of the maneuverability from the attacker missile， which was compensated for in the design of active defense LOS guidance law for the cooperation of aircraft and missile. The results of the simulation indicate that the method used in this paper can effectively defend the attacker missile with unknown maneuverability. The study in this paper thus provides a reference for the three-body attack and defense problem.