In this paper, an ontology representation of natural calamities based on the W3C standard is proposed. With understanding of the concept definition, naming and categorization, we logically represent the concepts of natural calamities with the Description Logic (DL) of the first-order logic. The logical representation is applied in the ontology design, in which the class-tree, collection of object properties and collection of data properties are built up, as well as the ontology library. We test the ontology library of the natural calamities built with the proposed representation in the soft real-time GIS mapping and web posting system. The performance of the automatic warning analysis of severe weathers proves the efficiency of the ontology representation.