Fluid-structure interaction is the science of investigating fluid flows interacting with structures. And the occurred phenomena in the interaction. Moreover, Fluid-structure interaction (FSI) has a wide range of applications in many engineering systems. We use the FSI model just for cases that fluid and solid behavior are completely coupled and the reason for stress in a structure depends on pressure distribution of fluid flow behavior. If pressure distribution around solid structural is uniform and by changing deflection is constant and is independent to fluid flow behavior, we do not suggest use FSI model because the complexity and computational cost of FSI simulation are higher than fluid flow analysis or structural analysis. Even some times is higher than the sum of total computational cost. So we suggest simulating the project by the FSI model just in non-uniform pressure distribution (based on fluid flow behavior) and in cases that by changing deflection pressure distribution will be changed.