Objective Try to find out the best graft-host diameter ratio and junction angle that can furthest improve success rate in coronary artery bypass graft(CABG).Method ANSYS9.0 was used to simulate CABG,and response surface methodology(RSM)was applied to construct the mathematical model,last theory of optimization was performed to search the optimum graft-host diameter ratio and junction angle which can make the primary factor influencing success rate-wall shear stress gradient(WSSG)to be the smallest.Result The model with large graft-host diameter ratio and small junction angle has better hemodynamics feature in CABG.Conclusion There are many factors influencing success rate in CABG,at present,it is advisable to adopt graft-host diameter ratio as large as possible and junction angle as small as possible with help of clinic experience.