Hepatic portal vein is an important vein in hepatic blood vessels system. To study the mechanicalproperties of the portal vein is helpful to the researchwork of hepatic rheology, and offers a usefultheory in artificial blood vessels, hepatic transplantation, portal hypertension and so on. By theresearch of the residual strain of rat portal vein so as to lay the fundamental of studying themechanical properties and for building the pathological animal model of rat portal vein.By obtaining the following parameters thickness of blood vessel wall at no-load state and theopening angle of blood vessel of zero-stress state it is able to calculate the circumferential residualstrain of blood vessel at no-load state. The experimental results showed that Ee outer wall ispositive Eiinner wall negative and the residual strain of hepatic portal vein is little because itsvessel wall is very thin