Background: It is proved that hemodynamic factor plays an important role in the process of initiation, growth and disruption of aneurysm. Objective: To observe the hemodynamic characteristics of intracranial bifurcation aneurysms which located in the bifurcation area by three-dimension computer numerical simulation method. Design, time and setting: Numerical simulation of three-dimension test was performed in the Endovascular Therapy Laboratory of Beijing Neurosurgical Institute in July of 2008. Participants: Two inpatients from Department of Neural Intervention, Beijing Tiantan Hospital of Capital University of Medical Sciences from April to July were selected. Case 1: Female, 37-year-old with anterior communicating artery aneurysm (coplanar bifurcating aneurysm), nonvisualization of anterior cerebral artery in A1 segment. Case 2: Female, 61-year-old with basilar artery apex aneurysm (non-coplanar bifurcating aneurysm). Methods: Aneurysm numerical model was constructed by three-dimensional angiography images, and reconstructed at the special work station of GE Company. The adjusted images were handled by the Matlab7.0 to generate STI file which further introduced into mesh generation software to obtain the three-D meshes of aneurysms. Then the computational fluid dynamics software (Fluent 6.0) was used to simulate the blood flow and analyze the hydrodynamics. Main outcome measures: The blood flow rate in inflow tract, outflow tract and top of aneurysm, dynamic pressure, as well as wall shear stress were observed. Results: The hemodynamic factors such as velocity, dynamic pressure and wall shear stress were the highest near the inflow tract, and lowest on the top of the aneurysm dome, there had significance compared with outflow tract (P < 0.05). But the dynamic pressure on the top of the coplanar aneurysm was higher with (62.385 3 ± 35.076 5) Pa. The wall shear stress on the top of the non-coplanar aneurysm was lower with (0.220 7 ± 0.071 6) Pa. Conclusion: The dynamic pressure plays a main role in the rupture of coplanar bifurcating aneurysm, while the insufficiency of wall shear stress results in the rupture of the non-coplanar bifurcation aneurysm.