Abstract: [Objective]Deepwater oil and gas fields are typically characterized by sparse wells, large well spacing, and limited seismic data resolution. The sand bodies of deepwater gravity flow reservoirs exhibit multi-hierarchical nesting, with complex spatial distribution and stacking relationships. Conventional modeling methods struggle to balance geological model rationality and model accuracy, posing significant challenges for reservoir characterization and modeling. [Methods]Taking the A Gas Field in the Baiyun Sag, Pearl River Mouth Basin as a case study, this paper proposes a geological modeling method for deepwater gravity flow reservoirs suitable for sparse well conditions. Under joint well-seismic constraints, this method adopts the core concept of "hierarchical constraint and level-by-level nesting". In the first-level modeling, the interpreted channel complex profiles are transformed into a 3D grid through a spatial mapping mechanism, and a combined deterministic and stochastic approach is employed to construct the channel complex model. In the second-level modeling, for the channel complex model, 3D training images reflecting the morphology and stacking relationships of single channels are constructed, and a multiple-point geostatistics algorithm is utilized to finely characterize single channels and mudstones. For the lobe-mudstone complex, an object-based modeling method is adopted to establish the mudstone model. Finally, sedimentary units at all levels are nested and amalgamated according to hierarchical priority to establish a 3D sedimentary facies model, based on which a reservoir petrophysical model is constructed. [Results]Application results demonstrate that, compared with deterministic modeling methods, the proposed method more accurately characterizes the heterogeneity and spatial distribution of sand bodies in deepwater gravity flow reservoirs, significantly improving model accuracy. [Conclusion]This method provides a reliable theoretical basis and technical support for the exploration, development, and decision-making of deepwater gravity flow reservoirs.