A improved multi-index evaluation model based on TOPSIS is proposed in this article to build an air combat effectiveness evaluation model. This New model improves the shortcoming that the traditional evaluation method can only make a comprehensive evaluation of air combat effectiveness on a macro level, but cannot make a micro evaluation by comparing different aircraft strengths and weaknesses. Different index systems have been established for the over-the-horizon and dogfight air warfare tasks, and according to the defects of subjective method and objective method when evaluating the weights of indicators, the combined weighting method is constructed by using the minimum entropy principle to synthesize the two different types of weighting technologies: structural entropy weight and entropy weight. The algorithm verification shows that not only can the combined weighting method reflect the different characteristics of the index importance degree under the two line-of-sight conditions, but also the improved model can correct the evaluation errors of the original model, indicating that the method proposed in this paper is feasible and effective.