Cardiovascular disease is the one of most important diseases for human in the developed countries and is responsible for millions of deaths and disabilities every year. In cardiovascular biomechanics, the fluid-structure interaction within large blood vessel is required to understand the aortic wall tear, aortic dissection and so on. Strongly-coupled methods yield the resolution of a nonlinear problem on the fluid-structure interface, which may be very time-consuming. A loosely coupled method was used to study the complex mechanical interaction under steady flow and pulsatile flow in a three-layered aortic arch model. The results showed the impact of steady flow and pulsatile flow, the variations of wall stress along arch portion, and wall stress distribution in three-layered wall.