Introduction: Arterial stiffness especially pulse wave shape index (Augmentation index: AIx) has attracted a great deal of attention as the predictor of the circulatory system condition. The AIx determined by the ratio of pulse pressure of reflection wave to progressive wave seem to show the change of reflection wave cause by the total peripheral vascular resistance. However, a phenomenon that progressive wave component increases and reflection wave component hardly changes during the cold pressure test (CPT) as a transient biological reaction. This phenomenon is hardly to explain only in the increase of the total peripheral resistance. Consequently, the mechanism of pulse wave change that attributes the reaction of the circulatory system was analyzed by using numerical simulation. Method: The model of the systemic artery constructed two cylindrical tubes with taper. These cylindrical tubes denote a main aorta of systemic artery from central aorta to common iliac artery bifurcation and a brachial artery form aortic arch to the bifurcation of radial and ulnar artery, respectively. Following parameters were varied which correspond to the CPT load, heart rate: HR, stroke volume: SV, aortic stiffness: AS peripheral resistance: RT and arterial stiffness of brachial artery: BT. Result: (1)A biological reaction of circulatory system during CPT is a complex reaction combined with not only peripheral artery but also heart or central aorta. (2)A biological reaction seems to be different by the short term CPT and by the long term CPT. We suspect that the change by the short term CPT may have caused β-effect and the long term CPT may have caused α-effect. (3)The pulse wave change phenomenon (especially change of AIx) during the CPT can be expressed using numerical simulation model combined with central aorta and brachial artery.