Shallow water flow ( SWF) can greatly influence the safety of deepwater drilling. In this study, the occurance and its potential risk of SWF on drilling safety in the northern slope of the South China Sea was analyzed based on SWF formation conditions and paleogeological characteristics. A numerical simulation model of SWF blowout was established, and the effects of the over-pressure, geologic parameters and the size of SWF formation, and penetration rate on water blowout were investi-gated. SWF hazards were then classified quantitatively according to water blowout rates. The results show that there are pa-leogeological conditions for the formation of SWF in the target area. However, the scale and pressure of SWF formations would be low so that there are low probabilities for serious SWF hazards to be confronted. SWF blowout is characterized with spontaneous release of water and pressure, and the water blowout rate and volume can be up to 70 m3/h and 60 m3 during drilling through a typical SWF formation with a formation pressure coefficient of 1. 15 using sea water as drilling fluid. SWF blowout is mainly controlled by its over-pressure and the size of the SWF formation.