In most studies of numerical simulation about Kawasaki Disease, vessel wall assumed to be rigid, although the real vessel wall has hyperelasticity. One of the reasons for that is difficulty to calculate the motion of fluid and hyperelastic wall (structure) simultaneously since fluid calculation is Eulerian while structure is Lagrangian. To solve this problem, the method to introduce the weight function to decide whether the calculation point is fluid or structure is effective. In this study, as a first step for revealing the inner phenomena of a coronary artery, we model it as a hyperelastic circular tube and calculate the inner flow with the above method to consider the interaction between the blood flow and structure, and investigate the necessity of assuming the hyperelasiticy on the vessel wall. In conclusion, the effect of the hyperelasticity is confirmed and it should be assumed to calculate the flow in a coronary artery.