Abstract: The formation, movement，accumulation ,and dispersion of oil/gas have close relation with palao-groundwater.So it is very necessary to study palaohydrogeologic problems of oil/gas-bearing basin,This paper first describes the characteristics of geology and petroleum geology, then classifies the palaohydrogeologic periods，and then analyzes palaohydrogeologic conditions of formation, preservation and disruption of oif/gas field in Biyang depression,especially the characteristics of palaohydrodynamic field during(and after) oil/gas formation stage, and the relation between palaohydrodynamic field and distribution of oil/gad dipoSits,It has been proved that palaqhydrogeologic

Key words: Oil/gas field, Palaohydrogeology, Palaohydrodynamic field, Biyang depression