The complex properties and genetic origin of soft soil in the Hexi area (west of the Qinhuai River) of Nanjing City need to be conducted with a comprehensive and systematic research in order to propose reasonable design and management measures for the constructions. In this paper, the sedimentary evolution of stratigraphic features, the microstructure and material composition of the soft soil, as well as the infiltration, compression, strength, sensitivity and creep properties were analyzed. It could be shown that the floodplain deposition environment and process of soft soil stratum in Hexi district were mainly closely related to the changes of river valley, which were deposited with a new age, with structures of low maturity, large variation of thickness, uneven distribution of sand interbed lens. Such type of soft soil could be concluded as underconsolidated mainly with clay minerals of illite, medium—high sensitivity and low—medium secondary consolidation characteristics.