Bongor Basin，located in the south-west of the Republic of Chad，is a Mesozoic-Cenozoic passive rift basin evolved under the influence of shear zone of Central Africa Rift. Bongor Basin was in the beginning of a rift lacustrine basin development and always kept expansion through a continuous transgression progress during the sedimentation of the P Formation，during which terrestrial fan delta-lacustrine deposited. The results of core observation show that the P Formation are characterized by near-provenance，deep-water，coarse-grain，gravity-flow and consecutive transgression sediments.Combined with the indication of well-logging and seismic data，it is determined that fan delta，lacustrine and gravity flow develop in the study area. The fan delta consists of fan delta front and pre-fan delta sub-facies，and the fan delta front consists of submarine distributary channel，estuary bar，interdistributary and sand sheet. Taking the sub-sag in the north slope of Bongor Basin as an example，it is concluded that two main provenance systems exist through coupling analysis of structure and sedimentation，where delta deposits along the long axis. There are two structure-defined sedimentary modes built along the short axis：fan delta grows in the structure-controlled（fault-connected）zone，while gravity flow grows in the nonstructurecontrolled zone.