Abstract: In view of short of drilling wells in the deepwater area of Qiongdongnan Basin (QDNB), a set of calculating methods for the fluid potential are established on the basis of accessible stack velocity and applied to the QDNB for the case study about the subsurface fluid (gas) migration. Faults and diapir develop widely and influence the distribution of gas hydrate. BSRs' development zones are consistent with the con-vergence belt of potential field strength. Gas hydrate can be classified into two types according to gas origins, which are deeper thermogenic and shallower biogenic. Most of the faults correspond to relatively low potential area, showing their open feature. These faults can serve as pathways for upward gas migration and thermogenic gas hydrate may be formed above them. The diapirs that developed near the structural uplift generally have relatively high potential and field strength directed outside. These diapirs bring lots of gas upward and provide an abundant gas source for the formation of gas hydrate.