Combat Modeling and Simulation (M&S) is significant to decision makers who predict the next direction of wars. Classical methodologies for combat M&S aimed to describe the exact behaviors of combat entities from military doctrines, yet they had a limitation of describing reasonable behaviors of combat entities that did not appear in the doctrines. Hence, this paper proposed a synthesizing modeling methodology for combat entity models considering both 1) the exact behaviors using descriptive modeling and 2) the reasonable behaviors using prescriptive modeling. With the proposed methodology, combat entities can represent a reality for combat actions rather than the classical methodologies. Moreover, the experiment results using the proposed methodology were significantly different from the results using the classical methodologies. Through the analyses of the experiment results, we showed that the reasonable behaviors of combat entities, which are not specified in the doctrines, should be considered in combat M&S.