Bayesian Network(BN) is a mathematical model based on probabilistic reasoning, which have a great advantages in solving the uncertainties between complex systems. Because of the complexity and uncertainty in air-combat, aiming at the problems in effectiveness evaluation, combined with the air-combat theory and reality. The effectiveness evaluation model of air-combat based on BN is build, the effectiveness evaluation method of air-combat based on BN is given, and simulation analysis is carried out. The results show that the model is valid and accurate, and the method has a strong ability to learn and reasoning.