Abstract: Taking the marine-continental facies soft silty soil in the Pearl River Delta region as the research object, the changing rules of shear strength and shear strength indexes under different consolidation pressures and degrees of consolidation were investigated through indoor straight shear tests, and a three-dimensional logistic mathematical model of shear strength and corresponding indexes-degree of consolidation-consolidation pressure was proposed. The results showed that: when P≥200 kPa, U≥40%, the growth of soft soil cohesion（c） and internal friction angle （φ） was more obvious; when U=100%, campared to the initial state, the soft soil shear strength （τ） under the action of all levels of consolidation pressure increased by 7. 89, 12. 73, 13. 50, 18. 20, 22. 38 kPa, respectively; the given three-dimensional mathematical model can directly calculate the shear strength index and shear strength under a certain consolidation pressure and consolidation degree; the research results can more accurately evaluate the overall stability of the soft soil foundation in this area during the step-by-step loading process.