Four aneurysms which were treated by flow diverter (FD) stents were simulated by using computational fluid dynamics (CFD). The objectives of this research were to find the characters of 2 fully successful cases among those 4 patients in terms of hemodynamic change after the FD was implanted. In CFD simulation, the FD stent mesh was represented by a porous medium layer with equivalent flow resistance. Results showed that for fully successful cases, after the FD was implanted both the blood volume flow rate and energy loss (EL) at the aneurysm were greatly reduced, but simultaneously the EL at the artery part did not appear alteration. For the unsuccessful cases, residual aneurysm was observed during the follow-up observation. For the large residual aneurysm, the EL at the aneurysm part was not decreased at the condition of high blood flow rates. On the other hand, for small residual aneurysm cases, although the flow rate and EL at the aneurysm were decreased, the EL at parent artery was increased.