One of the criterions to design the vehicle suspension system is the human comfort criterion. The human subjective perception is proportional to the vehicle acceleration respons and depends on the human vibration system. According to ISO 2631, the human subjective perception is characterized by peception variable.In this paper, the vehicle dynamic system is represented by four degree of freedom system with two points road roughness excitations with different time delay. The vehicle excitation model is developed from the measurement of real road roughness profile. The output of the analysis is the human perception variable according to ISO 2631. A shape filter is designed to realize the perception variable. The dynamic system is analysed by using the time domain method.