Background: The objective of this study was to evaluate hemodynamic patterns in end-side coronary artery bypass grafting with different anastomosis length by computational fluid dynamic study in the native coronary stenosis model. Methods: The fluid dynamic computations were carried out using ANSYS CFX. Incision length was set to be 2, 4, 6, 8, 10 mm. The angle between the two blood vessels corresponded to the length of the incision. Native vessels were set to be 90% stenosis. The radius of both native and graft vessels was set to be 2 mm. The inlet boundary condition was set by the sample of the transient time flow which was measured intraoperatively. Results: The energy efficiency was higher and energy loss was lower when the anastomosis length was longer until 8 mm. However, energy efficiency was lowest and energy loss was highest in the 10-mm model. In the 10-mm incision model, the streamline showed the scanty bypass flow in the bottom. Vortex showed that only 10-mm model showed the vortex just distal to the stenosis in the native inlet, and more vortex in native outlet than other length models. The oscillatory shear index (OSI) was higher in the outlet top in all models. And only 10-mm model showed high oscillatory index just distal to the stenosis. Conclusions: In the end-side anastomosis, an anastomosis length of 8 mm was the ideal length with less flow complexity, low OSI, and less energy loss and high energy efficiency in the native 90% stenosis model.