Ecological Sensitive Factors (ESF) and Ecological Sensitive Area (ESA) are significant to regional ecology. They are the important bases in regional planning and mass cities planning. This paper divides Ecological Sensitive Area into five types,from the vision of atmosphere,water,propagation,land,geology,and constructs an indicator system for Ecological Sensitive Area Division. Case study in Beibu Gulf (Guangxi) Economic Zone shows the division method used in mass cities area,which provides a standard method for Ecological Sensitive Area Division. The result of the case study analyzes some ecology problems in this area and provides ecology reference for later mass cities planning.