Abstract: The portland cement as a consolidating agent for increasing the strength of Soft cohesive ground and decreasing its deformation, already is widespread used in construction in the coastal area. Usually using dry powder mixing methed or deep bed stirring method for mixing portland cement into soft cohesive ground and reacting physico-chemically, we can get reinforce effect.This research project is supported by Jiangsu Province Science and Technology Foundation (Grant No. 91246). A comparative test for the cement soil samples in laboratory and in-situ, and macroscopic and microscopic analizes made us to the mechanism of reinforcing the soft cohesive ground with portland cement. A proposal on increasing the strength of soft cohesive ground, and economizing portland cement is putted forward.