To investigate the mechanical behavior and intrinsic characteristics of solidified silt soil under complex three-dimensional stress states, conventional triaxial tests, triaxial tests with constant intermediate principal stress ratio, and plane strain triaxial tests are carried out. The influences of confining pressure, intermediate principal stress ratio, and stress path on the stress-strain relationship, anisotropic strain development, and strength indices of solidified silt soil are systematically analyzed. The results show that the elastic modulus and yield strength of solidified silt soil are the largest under the condition of constant intermediate principal stress ratio, followed by those under plane strain condition, and the smallest under conventional triaxial condition. The soil exhibits obvious strain softening under conventional triaxial condition, while the degree of strain softening under true triaxial condition weakens with the increase of intermediate principal stress ratio, and no obvious softening is observed after yielding under plane strain condition. The cohesion and internal friction angle of the soil increase gradually with the rise of intermediate principal stress ratio. The mechanical properties of solidified silt soil present significant stress path dependence and intermediate principal stress effect. For practical engineering such as tunnel foundation pit excavation and underground structure backfilling, the corresponding test methods and mechanical indices should be selected according to the actual stress state of the foundation.