In view of combat effectiveness of air-to-ground autonomous attack for unmanned combat aerial vehicles (UCAV), an approach of autonomous attack based on succeed probability of assignment was proposed. Based on mathematic models of UCAV and guided bomb the exposed RCS of UCAV was controlled by lateral weaving maneuver with what the optimal attacking trajectory was designed. Through the pattern search algorithm, launch region was calculated and the way how to make another chance to release guided bomb was indicated. Via-ble autonomous attacking strategy was simulated through the analysis of combat effectiveness by the method of Markov dynamic simulating theory. The simulation result demonstrates that attacking trajectory is associated with the release mode of guided bomb. To increase the whole combat effectiveness, different attacking trajectories need corresponding release modes.