Based on the disturbed state concept (DSC) theory, a new constitutive model of saturated soft cohesive soil was presented through defining relative intact state, fully adjusted state and disturbed function for the saturated cohesive soil. Analyzing the mechanical characteristics of the typical saturated cohesive soil of Shanghai by consolidated-undrained triaxial shear tests, the relationship among axial stress, axial train and pore water pressure of the soil was obtained under different confining pressure. The constitutive model of cohesive soil based on the DSC theory was verified by the test results. The research shows that the theoretical analysis is in good agreement with the results of tests.