The unconsolidated-undrained shear strength of soft soil in the Yangtze river north shore were studied by three-axis non-consolidated undrained test, unconfined compressive strength test and quick shear test. The research results show that the soft soil in study area is the nonhomogeneous interactive marine soft soil deposited under the alkaline environment. Soft soil shear strength has inherent anisotropy. The soil system adopts a vertical cutting sample method, and the soil failure is along the 45°+ φuu/2 oval oblique shear plane by three-axis non-consolidated undrained test. The sample fracture surface is most concentrated in the range of 45.5°～ 46.3°. Using shear index by three-axis non-consolidated undrained test, the actual shear strength of the soil was calculated with the soil unit limit equilibrium theory. Average strength obtained by unconfined compressive strength test is less than the average strength of three-axis non-consolidated undrained test. This phenomenon is related to the stress state of failure and large frictional strength in study area. It explains the reason of high shear strength of soft soil in terms of soft soil particle composition, mineral activity and microstructure .