The patients with aortic aneurysm, especially aortic arch aneurysm, are prone to have aortic dissection. For investigation of the effect of aneurysm and wall stiffness on wall stress distribution, both the nonaneurysm arch model and the aneurysm arch model are constructed. The fluid structure interaction in the arch model of aorta was implemented. The results show the stresses are much higher at inflection points in aneurysm model than in nonaneurysm model, and the stresses at media in stiffened wall are higher than in unstiffened wall. The high composite stress is located at inflection points and is much higher in aneurysm model. The arch aneurysm and wall stiffening are important determinants of peak wall stress in aortic wall.