The whole body vibration suffering on the recumbent passengers in a railway sleeper carriage has a major impact on the comfort feeling. The vertical vibration model of the supine human body is studied. Based on the secondary suspension dynamic model of railway vehicles, a 14 DOFs “human-berth-vehicle” spatial vertical coupled dynamic model is established with consideration of the vibration isolation effect of the sleeping berth and the vertical vibration characteristics of the supine human body. Through random track irregularity excitation on the coupled dynamic model, the vertical vibration responses of the supine human body are studied at different train speeds. By applying the evaluation criterion of the vibration comfort of human body in supine position, the simulation flow for the vibration comfort of human body in railway sleeper carriages is established. The acceleration root-mean-square of head and buttock are weighted by body positions and frequencies in succession to get the vibration comfort index of the human body in railway sleeper carriages. Simulation software for the vibration comfort of the human body in railway sleeper carriages is developed. After inputting the structural and dynamic parameters of the human body and the vehicle, the simulating process for the vibration comfort of the human body can be carried out automatically. Therefore it provides an effective means to analyze the vibration comfort of the human body in a railway sleeper carriage and optimize the suspension parameters of the vehicle.