Abstract: AIM To investigate the mechanism of cardiovascular regulation by spectrum analysis of the variability of physiological variables. METHODS Two stress experiments (head up tilt and grip) were conducted and the association between the changes of heart rate variability (HRV) and blood pressure variability (BPV), and the activity of sympathetic nerve and cranial nerve was examined. RESULTS HRV and BPV contained information concerning cardiovascular regulation. CONCLUSION The regulation of HRV and BPV is in diverse forms and the measurement of the HRV reflects the regulation degree of heart autonomic nerve, not the tensity of heart non-autonomic nerve.