Urban spaces offer diversified and convenient living area. There are a lot of urban planning issues related to environmental protection, place redevelopment and disaster prevention after the 921 Earthquake. As we know urban vacant lands play an important function of green field, local preservation and disaster relief. However, traditional concept of urban planning focuses on land use regulations and tends to overlook surveying of detailed vacant land characteristics. Accordingly this study aims to classify vacant lands with disaster prevention mechanism in the Nan-tou city area where damage occurred during the 921 Earthquake. Considering the quake disaster prevention objectives objectives and quantitative index the classified results show 4 types of urban vacant lands: A. small area places located in the outer ring, underdeveloped and lack of disaster prevention potential and green field. B. large area places located in the CBD, fast developed with disaster prevention potential and green field. C. small area places located in corner parts of the CBD, slow developed and lack of disaster prevention potential and green field. D. small area places scattered around, fast developed and lack of disaster prevention potential. Finally we conclude that Type B requires proper regulation and induction of comprehensive planning, Type D requires integrated planning with disaster prevention and green field, and Type A and Type C can be retained and considered for green field development during urban planning review.