Abstract: THE PALEOGENE OF THE HAIZHONG SAG IN THE BEIBU GULF BASIN IS GENERALLY CHARACTERIZED BY THIN INTERBEDS OF VERY FINE-GRAINED SANDSTONE AND MUDSTONE, LACKING CONVENTIONAL LARGE-SCALE RESERVOIR BODIES, AND ITS SEDIMENTARY GENETIC MECHANISM REMAINS UNCLEAR. BASED ON DRILLING, LOGGING, 3D SEISMIC, AND PROVENANCE ANALYSIS DATA, THIS PAPER SYSTEMATICALLY INVESTIGATES THE TECTONIC EVOLUTION, SEDIMENTARY TYPES, PROVENANCE SUPPLY CHARACTERISTICS, AND FILLING EVOLUTION OF THE PALEOGENE IN THIS SAG. THE RESULTS INDICATE THAT: (1) THE PROVENANCE AREA OF THE HAIZHONG SAG IS LIMITED, BUT THE SEDIMENTARY EXTENT IS BROAD, FORMING A SPECIAL "SMALL SOURCE, LARGE BASIN" SOURCE-TO-SINK PATTERN; (2) THERE IS A WATER COMMUNICATION CHANNEL WITH THE ADJACENT WEIXINAN SAG. THE WEIXINAN LOW UPLIFT BECAME AN ONSHORE HIGHLAND FROM THE LIUYI MEMBER TO THE WEIZHOU FORMATION, INTERCEPTING COARSE-GRAINED MATERIALS FROM THE YUEGUI UPLIFT AND ALLOWING THEM TO DEVELOP EXTENSIVELY IN THE WEIXINAN SAG, WHILE FINE-GRAINED SUSPENDED MATERIALS (VERY FINE SAND, SILT, AND MUD) ENTERED THE HAIZHONG SAG THROUGH WATER EXCHANGE, ACHIEVING BLANKET FILLING ACROSS THE ENTIRE BASIN; (3) THE CONTINUOUS ACTIVITY OF THE NO. 3 FAULT CONTROLLED THE SUBSIDENCE CENTER AND ACCOMMODATION SPACE OF THE WEIZHOU FORMATION IN THE HAIZHONG SAG, WHILE SIMULTANEOUSLY LIMITING THE SIZE OF THE PROVENANCE AREA, RESULTING IN PREDOMINANTLY FINE-GRAINED SEDIMENTS; (4) DUE TO THE LACK OF COARSE-GRAINED CLASTIC INPUT, IT IS DIFFICULT TO FORM LARGE-SCALE RESERVOIR BODIES, AND THIN INTERBEDS OF VERY FINE-GRAINED SANDSTONE ARE THE MAIN RESERVOIR TYPE. THIS PAPER PROPOSES A SEDIMENTARY GENETIC MODEL OF "TECTONIC CONSTRAINT COUPLED WITH DISTAL SUSPENDED SUPPLY, " WHICH PROVIDES NEW INSIGHTS FOR THE STUDY OF FINE-GRAINED SEDIMENTATION IN THE HAIZHONG SAG AND SIMILAR BASINS, AND HAS GUIDING SIGNIFICANCE FOR HYDROCARBON EXPLORATION.