Past research on the vibration characteristics of automobile seat under horizontal vibration excitation is not deep and the simulation method of horizontal vibration is not novel. In order to improve the design level of automobile seat, the human horizontal vibration characteristics of man-chair system were studied with split car seat, which are designed and modified by ourselves, and ordinary car seat in this paper. The vibration characteristics of automobile seat under horizontal excitation were explored through the horizontal vibration experiment of man-chair system. The power density spectrum of vibration signal, acceleration weighted mean square root (AW) and acceleration vibration dose value (VDV),) were calculated by experiment for the calculation of the transfer rate curve of horizontal vibration signal. The results show that the improved split car seat, compared with the ordinary automobile seat, has a better shock absorption effect because the peak value of the split car seat is smaller, which shows the split car seat improves the comfort of the car seat to a certain extent. The results also show that the horizontal vibration transfer rate of the man-chair system reaches the peak between 2-4 Hz and gradually tends to smooth at 5Hz, and the peak value of head transfer rate is slightly larger than that of shoulder. In addition, this paper makes use of the mechanical system dynamics automatic analysis software ADAMS/LifeMOD to carry on the automobile seat horizontal vibration simulation experiment; Comparing with the horizontal vibration experiment, the results are consistent. The results are considerable for the design of automobile seat, and are important for the objective analysis of the horizontal vibration comfort of automobile seat.