This paper presents the sedimentary facies and architecture of the Qiantangjiang and Taihu incised valleys, and the characteristics of shallow gas reservoir distribution, based on the analysis of a large number of drillings, static sounding and chemical data obtained from the present Hangzhou Bay coastal plain. The result shows that, since the last glaciation, with variations in sea level, the development of incised valleys in the Hangzhou Bay area underwent three stages: (1) deep-cutting stage; (2) rapid-filling stage; and (3) rapid-burial stage. The fall of global sea level during the last glacial maximum enhanced the fluvial gradient and river cutting, resulting in the formation of the large-scale Qiantang River and Taihu incised valleys, and were subsequently filled and rapid-buried in the post-glacial period. with the paleointerfluve being exposed to air on both flanks of the incised valley. The sediments of the incised valleys show an upward-fining succession, and can be grouped into four sedimentary facies: gravel lag-deposit of in-channel to partly over-bank deposits of a meandering river, floodplain-estuary, estuary-shallow marine, and estuary sand bar, based on lithology, paleontology, and sedimentary textures and structures. Because during the deposition of the floodplain-estuary facies, the conditions of sea level rise, tidal regime, sediment supply and accommodation space were suitable for the development of a tidal ridge system, the sand lenses associated with this facies may represent tidal ridge formation in the incised valley. For estuary-shallow marine and estuary sand bars, because the sedimentary conditions are no longer favourable, no sand ridge deposits were formed. All commercial biogenic gas is stored in the floodplain-estuary sand lenses of the incised valleys.