Abstract: By means of core description, thin section analysis, paleontology identification and other analytical and testing methods, combined lithofacies and petrochemistry analysis technology, lithologic combination,paleo-fossils and other comprehensive division of stratigraphic structural units, the genetic mechanism of basaltic volcanic breccia reservoir in Dawa area of Liaohe sag was studied. The results show that the basaltic volcanic breccia is formed rapidly after quenching and cracking because of the underwater eruption of basalt.Reservoir space is mainly composed of residual breccia inter-porosity, followed by pores, dissolution holes,cracks, etc., which are medium-high porosity and low permeability reservoirs. The determination of the underwater eruption environment has raised doubts about the original Mesozoic stratigraphic division scheme,and it is believed that the basaltic volcanic breccia strata should be classified to the tertiary member of the Cenozoic.