Abstract: Based on the obtained water retention curves, the relative coefficients of permeability of Shanghai soft soil are predicted. At the same time, a series of tri-axial tests have been carried out for the analyzing of unsaturated strength of Shanghai soft soil. Results show that, the air-entry value for Shanghai soft soil (silty clay、clayey silt ) is about 110~250kPa, the residual suction value is about 10~20Mpa, and both of them decrease with the particle size increasing; the WRC for desorption process of Shanghai soft soil shows clearly in step-phase; for the lower suction range (0~1400 kPa), the water retention curves for Shanghai soft soil(layer 21) show significantly in hysteretic loop; coefficients of permeability of Shanghai soft soil changes nonlinearly with suction(water content), and it decreases with suction increasing(water content decreasing); for lower suction, the tri-axial strength for unsaturated Shanghai soft soil linearly increases with suction, and the tri-axial shear coefficient φb for Shanghai soft soil (layer 4)is 10.6°.