Abstract: The origin of Qiongzhou Strait has 3 causes:coast erosion, tectonic rifing and marine transgression. And the time for Hainan Island and Leizhou Peninsula to separate from each other also has some explanations:Pliocene, the beginning of Quaternary, before middle Pleistocene, after middle Pleistocene and Holocene. The latest data about the geology, oceanography and regional palaeo-biogeography of Qiongzhou Strait are analyzed in the paper, and it is thought that Qiongzhou Strait is not a rift. It grew out of a normal low land, and was formed in the middle Holocene, about (10 570±560)~(7 125±96) aBP, when marine transgressed the original normal low land. It is inferred that the average speed of central trough valley undercutting is 0.7 cm·a^-1, and the average speed of tidal current delta accumulation outside the west mouth is 0.17~0.31 cm·a^-1 after the Qiongzhou Strait formed.