Abstract: After offshore oilfields enter the middle and late stages of development, they generally face core developmental challenges, such as ambiguous characterization of internal connectivity of composite sandbodies, insufficient matching degree of injection-production well pattern, and unbalanced production degree of remaining oil. Therefore, the dissection of internal heterogeneity and architectural hierarchical structure of composite sandbodies has become a key issue of offshore oil-gas geological research. Based on high-quality offshore seismic data, we analyzed the sand group-level sedimentary microfacies by adopting the technical idea of “well and seismic data combination, with seismic data as the key”, fully explored the lithological and reservoir response information contained in seismic waveforms, and at last established a composite sandbody architecture dissection process from single well to a section then to a plane. The research results have successfully guided the compilation of oilfield development plans. Taking the braided river delta sedimentary system of Lufeng A Oilfield in the Pearl River Mouth Basin as the research object, this study shows that the composite sandbodies in this oilfield developed mainly two types of seismic waveforms (single-peak and double-peak) in single wells. By seismic forward modeling, the seismic waveform response laws of different sandbody combination styles were clarified. At the inter-well scale, the composite sandbodies mainly developed four types of architectural types: stacked, laterally stacked, isolated, and interchannel bay, showing obvious zonal distribution characteristics. The near-source area was dominated by stacked-connected contact channel complexes, the slope area developed laterally stacked-weakly connected channel complexes, and it gradually transitioned to isolated channels towards the center of the lake basin. This study provided an important geological basis for remaining oil potential tapping and developmental effect improvement.