Objective Saphenous vein graft (SVG) and left internal mammary artery (LIMA) are used to bypass with or without ligation of the coronary artery aneurysm (CAA) . Hemodynamics of bypass grafts are calculated by using the computational fluid dynamics (CFD) method. Hemodynamics can provide reliable help for clinical surgery about hemodynamic basis. Methods The 3 D models were established. SVG and LIMA were chosen as bypass grafts with or without ligation of CAA, respectively. Lumped parameter model (LPM, zerodimensional, 0 D) of cardiovascular system was established. 3 D models were coupled with 0 D model to calculate the hemodynamics of bypass grafts. Hemodynamics parameters included wall shear stress (WSS) , oscillatory shear index (OSI) and mass flow rate. Results The total mass flow of LAD was about 82 m L/min.OSI on graft of model 1 was 0. 014044. OSI on graft of model 2 was 0. 283494. OSI on graft of model 3 was0. 013035. OSI on graft of model 4 was 0. 023 263. The average WSS on the graft of model 1 was 0. 474 5 Pa in a cycle. The average WSS on the graft of model 2 was0. 8600 Pa in a cycle. The average WSS on the graft of model 3 was 0. 4424 Pa in a cycle. The average WSS on the graft of model 4 was 1. 699 Pa in a cycle. Conclusions Hemodynamics of the SVG were good with or without ligation of CAA. When selecting the surgical procedure with SVG, with or without ligation of CAA both may provide better surgical outcomes. Hemodynamics of the LIMA were good with ligation of CAA. However, hemodynamics of the LIMA was not good without ligation of CAA. The OSI was high and graft flow was low.The competitive flow was high. These abnormal hemodynamic parameters could cause bypass grafts becoming invalid. When selecting the surgical procedure with LIMA, research suggests that ligation of CAA may provide better surgical outcomes.