Abstract: Important sporadic events could lead to social chain response and serious consequences, which may endanger social stability. When an sporadic event occurs, the emergency preparedness should be generated in time to launch action, what will reduce losses in great extent. This paper researched on applying case expression and similarity measure methods to the emergency decision support based on Case-Based Reasoning, and proposed a new case retrieving method based on semantic distance synergetic mode. Three approaches are attempted to build the appropriate similarity measure: firstly, case features are extracted under semantic distance; then, case concepts are descripted under Multi-Case Multi-Label by various words with the same meaning; finally, similarity measure by wordnet, which would reason the most same semantic word. The experiments showed that the proposed method could significantly improve the case retrieving efficiency, which could provide effective and timely decision-making support for the future treatment of important sporadic events.