Objective To observe the dynamic changes of opening angle in zero-stress state and the relationship between tension stress (T) and extension ratio (λ) in longitudinal extension of the portal vein during the pathogenesis of intrahepatic portal hypertension, and investigate the role of biomechanical properties of the portal veins in the process of the portal hypertension. Methods The models of intrahepatic portal hypertension were established in SD rats by means of carbon tetrachloride (CCl4) injection. Opening angle, the relationship between T and λ in longitudinal extension of the portal vein were determined in 2, 4, 6, 8, 10 weeks after CCl4 injection. Meanwhile the changes of several hemodynamic indexes such as portal venous pressure (PVP), portal venous flow (PVF), mean arterial pressure (MAP), portal vascular resistance (PVR) and splanchnic vascular resistance (SVR) were detected. Results After CCl4 injection, hemodynamic indexes in the CCl4 rats had changed markedly. Accordingly,opening angles, Parameter b in longitudinal extension were increased. At the tenth week, they were much greater than those of corresponding controls (P<0.05). Conclusion The portal hypertensive rats were in hyperdynamic circulatory state (HCS). Changes of biomechanical properties of portal vein can be induced by HCS.