In this study, the growth-strain method was used for shape optimization of flow systems. It optimizes a shape by making a distributed parameter such as dissipation energy uniform in a flow system. In order to overcome the instability that occurred in the numerical analysis by the growth-strain method, the equation of bulk strain has been modified. And the distributed parameters were variously established in this study. By comparing the optimized shapes with the known optimal shapes for two flow systems, it is confirmed that the modified growth-strain method is very efficient and practical in shape optimization of flow systems.