Urban soil water “reservoir” can not only supply water to plants, but also minimize flooding risk by holding and adjusting soil water balance. Surface sealing during urbanization can weaken soil environmental buffering function which is very important to urban eco-environment. This study estimated the total soil water storage capacity, available water storage capacity, short time water storage capacity and invalid water storage capacity based on the saturation moisture content, field water moisture capacity and wilting point moisture content of different compacted soils in Nanjing. The results showed that with the increase of urban soil compaction, the total soil water storage capacity, available water storage capacity and short time water storage capacity reduced gradually, but the invalid water storage capacity increased gradually. As urban soil compaction is ubiquitous, its ability in discharging and holding water reduces, which often causes rapid urban flooding. In general, more open space with suitable soil condition is needed for an ecologically-sound urban environment.