In order to prevent the overall urban environment from worsening and realize the harmonious and sustainable development between city and nature, explorations on the ways of protecting and making use of mountains in city have increasingly become the focus point of planners. Yantai is a city with typical landscape pattern, so it adopts the way of delimiting the green line in the planning and implementation level to protect the damaged mountains and improve the overall urban ecological environment. Adopting the GIS analysis method, it obtains a comprehensively theoretical analysis line of preserving the mountain green space by conducting analysis in terms of the line of natural mountains, the function line of ecological service for city and the line of management. The theoretical line was fi nally revised to be a delimiting line with practicality for mountain green space.