Natural disaster emergency plans describe the domain knowledge of natural disaster emergency and it is the basis of high-efficient emergency response. However, most of the current emergency plans exist in the form of unstructured text, which hinders decision makers from obtaining emergency knowledge quickly and accurately. For the above problem, based on the analysis of disaster emergency plans and organization coordination processes, this paper proposes an ontology-based knowledge representation method for natural disaster emergency plans. Finally, many efforts are made for the actualization of the emergency plan digital management system of natural disaster. The result shows that this method provides valuable reference to the formal representation of emergency plan.