In cardiovascular biomechanics the fluid-structure interaction within large blood vessel is required to understand the aortic wall tear, aortic dissection and so on. A loosely coupled method was used to study the complex mechanical interaction under pulsatile flow in a three-layered aortic arch model. The results showed the variations of wall stress along arch portion, and wall stress distribution in three-layered wall. The study provide insight into the biomechanics of aortic dissection: at systolic acceleration phase, the highest normal stress in the media layer may be responsible for the tear and dissection extending into the media layer; at foot entrance flow, the shear stress might contribute to the dissection in the media near the adventitia layer.