In this paper,we take some examples of strong earthquakes as case studies to discuss the application of gravity observation in earthquake prediction in the period of earthquake preparation,co-seismic and post-seismic stages through study of the variation characteristics of gravity field,regional gravity field and its relationship with strong earthquake activity. Before the strong earthquake,the regional gravity field shows orderly change in a large range. The local gravity anomaly area related to the earthquake preparation is generated near the source area,and a significant gravity change gradient belt appears along the main seismogenic structural fault zone in the area. The strong earthquake generally occurs near the turning of the high gradient belt of gravity field change or the four quadrant distribution characteristic center. The dynamic variation image of gravity field can clearly reflects the information of gravity change in the process of strong earthquake preparation,development and adjustment. Based on the study of earthquake cases,the basic model of “field-source-belt” of gravity change before strong earthquake is put forward. Finally,the problems in the development of gravity monitoring and prediction in China are pointed out,and the prospect of using gravity monitoring data to carry out earthquake prediction and prediction research is discussed.