Based on fictitious soil pile and generalized Voigt model，dynamic equilibrium equations of pile and cushion cap were established in the vertical vibration，displacement and velocity solutions of cushion cap were obtained on frequency and time domain，and the influence of pile subsoil on the vertical dynamic characteristics of cushion cap was studied. The results show that under the same initial displacement condition，the deeper thickness of single-layer pile subsoil results in the smaller displacement，velocity amplitude and vibration frequency of cushion cap，but the resonant frequency is the same. In the case of weak substratum，the deeper thickness of substratum and the worse substratum results in the smaller displacement and velocity amplitude of cushion cap. Finally，the comparison results with single Voigt model of pile subsoil and actual engineering curves show that fictitious soil pile model can accurately simulate the role of weak substratum and the calculation is more close to the measurements.