According to the maneuvering of an Unmanned Aerial Vehicle (UAV) when escaping from the attack of pure proportional guidance air-to-air missile, the pursuit-evasion mathematic models of the UAV and the missile were built up in three-dimensional space.The potential fields of the UAV and missile were analyzed by using artificial potential field theory.The situation model, pointing to the fastest increasing direction of UAV combat power potential, was established.A new combined escape guidance law was formed based on anti-proportional navigation guidance and anti-tail potential field power.Simulation was made for the cases of head-on attack scenario and stern attack scenario.The results indicate that the guidance law can complete escaping task effectively.