Abstract: The Lishui-Jiaojiang Sag was a faulted basin developing on the continental margin from the late cretaceous epoch. The ex-tensional quantities, coefficient and ratio of the basin in differ-ent areas during the different faulting time of extension have been obtained by means of the technique of balanced geological cross-sections in this paper. The basin’s extension differs in dif-
ferent period and different regions. The extensional ratio re-duces from the south to the north. The main extensional period is from the late Cretaceous Epoch to the Paleocene Epoch and maximum extensional period is different in different regions.The maximum extension period is the late Cretaceous in the
south Lishui Sag, the early Paleocene in the north Lishui Sag and the Jiaojiang Sag. The basin’s extension results from the normal faults’drawing away in horizon and the faulted blocks’tilting extension.

Key words: Lishui-Jiaojiang Sag, extensional activity, ex-tensional quantity, balanced geological cross-section