<p>The loading of soft soil embankment is prone to form strong excess pore water pressure, which will weaken the mechanical parameters of soft soil subgrade and affect the long-term settlement stability of the subgrade. This paper conducted an experimental study on the mechanical properties of soft soil under excess pore water pressure. A soft soil embankment in Shenzhen, China, was selected as the research subject in this study. Here, the influence law of excess pore water pressure on stress–strain, strength parameters, and pore pressure coefficient of soft soil was analyzed. The results revealed that the stress–strain curve of soft soil is characterized as strain hardening under excess water pressure and cohesion is more easily weakened by pore pressure than the internal friction angle. Excess pore water pressure significantly reduces the deformation modulus of soft soil, particularly under low confining pressures. Excess pore water pressure reaches the peak and gradually tends to be stable when the axial strain is 8%; while at the strain of 4%, the pore water pressure coefficient reaches the maximum and then gradually decreases and tends to be a stable value: 0.075–0.11. The conclusions in this study can provide a theoretical reference for the prediction of excess pore water pressure of soft soil foundation and the analysis of the long-term settlement.</p>