We tested the thoracic aortas of spontaneously hypertensive rats(SHR)and Wistar Kyoto Rats(WKY)about diameter,thickness,strain-stress and relatively stretch length at fragility time.According to Lagrangian meaning and straight stretch theory of Feng Yuanzhen, we discussed the strain-stross and got the experience fomula:dT/dλ=α(T+β)=αT+ E0,which was used to assess the vascula's boimechanics of SHR and WKY in hypertension and aging.It is show that not only the vesscle's relatively stretch length of WKY is more than SHR'S, but also young than old(P<0.01,P<0.05).The vasculas of SHR and aging have higher elastic modulus.Always,the elastic protein and smooth muscle play an important role at the lower strain and the collagen fiber at higher strain.It is considered that the thoracic aortas in SHR and aging having higher elastic modulus are due to the decline in elastic protein.