A type of high fertile paddy soil is developed under the culrivation of double-crop rice the alluvial deposit of delta region Chu-Kiang.As resulted from high fertilization by manures and mudds and also from the long-time submerged condition, about 8 months in one year, these soils contain small granulars(0.005-1 mm. according to Kachinski method) around 20% and organic matter 2.5-3.5%,with average C/N ratio 11.6.