Not only the price of a steam cleaner but also the performance of it should be considered to improve the competitive power of the products. In this study, a steam duct was optimized by changing the length of guide line for compensating the drawback of the unbalanced mass flow rate of steam from each outlet. For evaluating the mass flow rate of each outlet, a commercial CFD(computational fluid dynamics) code was used. In the process of the optimization, SQP(sequential quadratic programming) optimization algorithm was applied. The numerical method in this study can be widely used to develop a high performance domestic steam cleaner.