Cohesive soil of the interactive marine & terrestrial deposit along the north side of the Yangtze River estuary has poor physical properties in which water content ratio is approximate or excessive to liquid limit and void ratio is approximate or excessive to one. With free piston thin wall sampling technique and vacuum freeze drying method, undisturbed and remolded samples in different consolidation stress were made. And the microstructural and parameters were analyzed. It was found that the microstructure change and macromechanic properties were in good agreement. And micromechanism of the abnormal correspondence was found between the poor physical properties and good mechanic characteristic indexes of structural cohesive soil.