In this paper, we present an air combat decision-making method based on situation assessment, which is realized by Dempster-Shafer Evidence Theory (D-S Evidence Theory). For fusion calculation by D-S evidence theory between the elements of confrontation, we take into account factors of air combat such as geometry relationship, perception and attack capability of Unmanned Aerial Vehicle (UAV) fighters. On this foundation, we use UAV maneuver planning strategy and maneuver database to realize UAV air combat decision making method. At Last, we validated the method by a typical simulation scenario of UAV air combat.