Abstract: For the existing ontology concepts similarity measuring methods cannot describe the fuzzy features of concept,based on the semantic structure information of ontology,a method which describes the features of the concept by semantically expanded set is proposed,then a fuzzy set is defined based on the semantically expanded set. As quantifing the features,the algorithm considers influence of asymmetry,depth and local density of ontology concepts on similarity computation.Finally,the semantic similarity between two fuzzy sets is used to measure the concepts similarity of ontology.The result of experiment on a commonly used dataset indicates that our method outperforms traditional similarity measures.