Objective To study the blood flow in aneurysm and its influence on mechanical properties of vascular walls for two kinds of common aneurysms, so as to improve the diagnosis and treatment of aneurysms and the prognosis of patients. Methods The interaction between the aneurysm-carrying vessels and blood of two common aneurysms was studied by fluid-structure interaction method. The blood flow velocity, wall deformation, stress distribution and damage form of aneurysm-carrying vessels were analyzed. Results The blood flow in both aneurysms were slow and stable, which resulted in better deposition and adhesion conditions. The junction between the aneurysm and the downstream of the blood vessel was a dangerous place for damage. The spindle aneurysm would undergo shear failure on outer wall of the aneurysm, while the cystic aneurysm would undergo stretching failure on inner wall. Under the effect of the same blood flow, a larger stress appeared on the cystic aneurysm, which was more prone to damage, and the tensile failure would lead to a more serious consequences. Conclusions The junction at the aneurysm and blood vessel is prone to damage, and the cystic aneurysm is more dangerous and harmful.