The main problem of military antagonism decision is its difficulty to confirm the strategy set of adversary. This research analyzes the military decision under the uncertainty of strategy set based on hypergame. The decision approach of high-level hypergame was proposed after analysis the belief relationship of each level. The result of high level was put back to low-level to refine the decision based on the analysis of the possible decision of adversary. Consequently, this makes decision of friendly forces more pertinent and reasonable against to adversary. Finally an example is used to illustrate the approach.