Abstract: An earthquake occurred in the study area in 1605,with a magnitude of 7.5,which caused the continental collapse to have formed the sea.For this area the seismicity is characteristic of 1)clustering in the north and south of the Hainan Island;2)migrating south-north;and 3)a definite seismic period.These kinds of formed characteristics may be related to the crustal isostatic disequilibrium responding to the uplifting of this island in the process of being deformed between the Eastern Asian continent that spreaded south and the South China Sea that was compressing as it opened.