In order to make commanders at all levels consistently understand the enemy campaign at some stage and its execution, in-depth study on formal description method of enemy campaign operation action (ECOA). Based on understanding the process and essential of situation assessment, the frame of ECOA based on knowledge discovery is presented, and formal definition is put forward by using six-tuple array. Then detailed describe the concept attribute set and its hierarchical relationships of ECOA, and the ontology model of ECOA based on UML is carried out. The result shows that the research can express the whole characteristic of one EOCA, and realize share battlefield situation.