Most present studies on the plastic strain of soft soil under traffic load ignored the trains leaving intervals. Thus, a series of triaxial undrained dynamic tests including continuous and discontinuous vibration on the undisturbed soft clay consolidated along K₀ line were carried out, considering different relative deviatoric stress levels and different stop-vibration ratios. The purpose is to study the strain development of undisturbed silty soft clay under long-term intermittent cyclic loading. Analysis results of the continuous vibration test show that the relative deviatoric stress level has no effect on the relationship between the normalized plastic strain growth rate and the vibration times, and only affects the equivalent initial strain. The normalized strain growth rate is significantly reduced, and the vibration times required to be stable are reduced, due to the increase of the strength during the intermittency period. The influence law of the stop-vibration ratio on the normalized plastic strain growth rate was analyzed based on the fitting result of hyperbolic function, and results show that the shape parameter of the curve of normalized strain growth rate versus vibration times is linearly related to the stop-vibration ratio. A long-term strain prediction model considering intermittency effect was established. The model consists of two parts, the equivalent initial plastic strain and the normalized growth rate. This model is proved to work well, and is helpful to calculate and analyze the long-term strain of soft soil foundation under subway load.