Cerebrovascular diseases are one of the three major mortalities, such as the rupture of cerebral aneurysm. The formation and growth mechanism of the cerebral aneurysm has not been clearly understood. Treatment decision of incidental intracranial aneurysms is complex. Currently, however, there is no certain quantitative method to evaluate risk of rupture. We utilized Computational fluid dynamic (CFD) technology to understand difference of hemodynamic condition between stable unruptured aneurysms and those that ruptured during the observation that followed. The hemodynamic characteristics; energy losses (EL), were calculated under 100 aneurysms and the results indicated that there are more than five times difference from ruptured and unruptured aneurysms. According to flow visualization, the flow inside ruptured aneurysms appeared stronger impact on the aneurysm wall. On the contrary, the flow inside unruptured aneurysms passed smoothly and quickly through the aneurysms. The mean average recirculation time of ruptured aneurysm was two times higher than that of the unruptured ones. These results indicate that EL and recirculation time may be an useful parameter to quantitatively estimate the risks of ruptured of cerebral aneurysm.