Driving mental fatigue is a substantial problem and threatens people's health and life. This investigation was made to evaluate the driving mental fatigue based on power spectral analysis of heart rate variability (HRV) and blood pressure variability (BPV) synthetically. Twenty health male subjects (28.8 +/- 4.3 years) were required to perform the simulated driving for 90 min. The frequency domain indices of HRV such as low frequency (0.04-0.15 Hz, LF), high frequency (0.15-0.4 Hz, HF), LF/HF together with the indices of hemodynamics such as blood pressure (BP) and heart rate (HR) of the subjects were calculated and anlyzed after the simulated driving. The results showed that sympathetic activity of the subjects enhanced after the simulated driving while parasympathetic activities decreased. The sympathovagal balance was also improved. Remarkable linear correlations were observed between all the corresponding indices of HRV and BPV (P<0.05). The findings suggested that the evaluation of autonomic activities by means of multi-variable synthetic effect analysis is scientific and objective.