Abstract: There are many difficulties in petroleum exploration on the structure B of Sag A in the East China Sea Basin. Many basic geological problems in the middle and deep parts of the field need to be solved, which include the unclear distribution of the sedimentary systems and reservoir sweetness. Combined regional geological survey together with drilling wells, the study of seismic sedimentology and full-band information analysis were carried out based on the broadband seismic data. The results suggest that there were three large meandering river channel systems in the eastern, central and western parts of the structure B respectively during the depositional period of Member C. Three typical frequency anomalous zones were found in the central and western channel systems and the petroleum detecting technology confirmed that they are potential gas-bearing structures. The research shows that the Member C in structure B is a structural-lithologic reservoir controlled by a large meandering river system.