A model of similar coupled acoustic field consisted of the engine room and the driver room was established. The effects of the energy self-lost factor and the firewall thickness of the engine room on the acoustic energy of each subsystem were studied with the statistic energy analysis method. Subsequently, the parametric sensitivity analysis illuminated the energy varying characteristics with respect to the energy self-lost factor and the firewall thickness of the engine room. The results provide a reference for the parameter optimization during automobile design.