Abstarct: Nowadays cardiovascular disease are one the most important cause of death in the world. These kind of disease consist of heat disorders or vessel stenosis and aneurysm. Stenosis can disrupt blood pressure and harden vessel wall and if rupture occurs it may increase the risk of heart and brain strokes. So in this field for prevention and treatment many studies have been done. In this study, pulsatile blood flow through stenosed vessel is simulated and the effect of reduction and mechanical properties of diseased vessel on hemodynamic parameters are investigated and the results are reported. Since the scientists claimed that non-Newtonian models are suitable for simulating body tissues, we benefit from Casson model for simulating blood flow and for vessel wall viscoelastic models including Maxwell, Kelvin-Voigt and Generalized Maxwell are used. In addition for solving fluid and solid domains at the same time we use from FSI(Fluid Structure Interaction) approach. The aim of this study is to investigate hemodynamic parameters in blood flow through stenosed vessel with 25, 50 and 75 percent of severity respect to diameter and to compare and analyze the results between different severities. Our work innovation is the use of multilxayer vessel wall which if we divide the wall into two parts of healthy and diseased, the healthy part consists of three main laxyers including intima, media and adventitia and the diseased part consists of fibrotic intima, diseased media, adventitia, lipid and fibrous cap. So in addition to the comparing the results between different severities, we compare hemodynamic parameters between models with and without lipid core and in all of these cases the blood velocity and pressure, wall shear stress and radius displacement are investigated and discussed. Also vortex and backflow regions are studied. To speak more general about non-Newtonian models, in this study some models with Newtonian blood flow and elastic walls are simulated and their results are compared with the non-Newtonian ones. In all of these models with the severity increase velocity profile dramatically increases. And the pressure difference between the upstream and downstream increases. Maximum of wall shear stress and minimum of radius displacement occurs at the peak of severity. Also formation of vortex and the backflow are clearly visible in 50 and 75 percent of severity.