Abstract: Based on the distribution of focal depths, there is a 'v-shaped' focal zone bottom beneath southeastern sea area of Taidong county, Taiwan, that is, in the area of 123°30-123°00E, 22°-23°N. Such kind of particular structure caused a series of strong earthquakes, forming another concentration area of strong earthquakes besides Hualian, and formed an intermediate focus (70-170km deep) area which is race in Taiwan Region.The characteristics of the 'v-shaped' focal zone in plane are that the focal isobaths of intermediate focus earthquakes form three SN striking oval traps at the same center, and its sectional characteristics show that the bottom of the focal zone is a 'v-shape'.The direction of focal dip affects prediction of future earthquake disasters. Basing on that foci in Taidong area are dip to outside principally, that is, to the east, so the epicenters mainly lie on the sea area, that is distant from the land.Combining with small population and race large construction projects, authors think that it can be classified as anon-priority arsa of earthquake prevention and disaster reduction.