In order to study the microstructural mechanism of Shanghai soft soil under consolidation,the fourth layer of Shanghai soft soil under different consolidation pressures were tested by high resolution field emission scanning electron microscope. The results show that with the increase of consolidation pressure,void ratio decreases significantly during the initial period,and the soil density increases. Average form factor increases significantly,the smooth degree increases significantly. The probability entropy decreases gradually,the orientation and order of pore arrangement are enhanced. Consolidation pressure changes pore characteristics including scale,pattern and arrangement significantly,and the microstructure parameters can preferably reflect the macroscopic mechanical properties.