Abstract: How to provide the targeted effective data rapidly for users according to operational task demands is one of the problems that must be solved once battlefield environmental data guarantees to realize active service. Aiming at the complex incidence relation between operational tasks and battlefield environment data, it lacks the methods for the problems such as data matching semantic expression and quantified semantic correlation and semantic weight of different elements at present. Therefore, a calculation method on semantic similarity of battlefield environment elements based on operational task ontology is proposed. The logical relationship of conceptual semantics between operational tasks and battlefield environment data is confirmed with ontology method. The battlefield environment elements are divided according to task semantic relevancy, and the semantic similarity calculation is established through adopting the reasoning techniques of the combination of rules and cases. Thus we can quantify the entity semantic weight of battlefield environment elements. Experimental results demonstrate the feasibility of this method which can effectively improve the organization efficiency and precision of battlefield environment data.