Domain ontology plays an essential role in formalization and sharing of domain knowledge. However, constructing domain ontology is a labour intensive and time consuming engineering. To efficiently represent knowledge as a set of concepts and relations within domain ontology, a 5W1H method is proposed to analysis concepts and relations of it from six aspects including Who, When, Where, What, Why and How. The theory and methodology of modelling domain ontology based 5W1H is also presented in this paper. Take Expert Ontology in expert information domain for an example, six-layer framework for conceptual model of expert ontology based 5W1H is designed, and conceptual model of expert ontology is constructed, in which concepts and relations within expert ontology are defined. Application shows that the 5W1H modelling method is flexible and scalable, because it is not only able to assist ontology engineering to construct domain ontology quicker and more accurately, but also adaptable to business changes and user requirements. In addition, it is helpful to define reasoning rules for inferring knowledge and to share domain knowledge.