Abstract: Abstract: The design of a hydro turbine's runner involves many disciplines, such as fluid, structure, strength and so on. As the hydro turbine's capacity increases, the owner of a power plant has strengthened the demand for the turbine's stability. But the traditional sequence design method has difficulty meet ing the demand of the design requirements. So it is necessary to establish a new optimization design method called the multidisciplinary design optimization method, which can consider the interaction of each discipline. At present, the optimal design method of a hydro turbine's runner still can not combine each discipline perfectly in design process. It is necessary to carry out the research about multidisciplinary design optimization (MDO) design method of hydro turbine's runner. Based on the research findings of other fields about multidisciplinary optimization, this paper draws the MDO design method into hydro turbine's runner design, and carries out a preliminary study on the turbine runner's MDO design method. On the basis of design characteristics of a hydro turbine, an optimization design system has been established according to the multidisciplinary method in this paper. This optimization design system could improve the runner blade's hydraulic performance and structural strength simultaneously. In addition, a parameterized module based on the Bezier curve, auto mesh module, computational fluid dynamic module, and finite element analysis module were integrated in the system. The system automatically completes geometry modeling, mesh generation, and multidisciplinary performance analysis. This system uses the geometric shape parameters of a runner blade as optimization variables, and the hydraulic efficiency and maximum stress of runner blade were used as objective functions. The NSGA-II algorithm was used to carry out the optimization. In order to reduce the time of optimization and increase this method's practicability, the calculation method of weak coupling was used for multidisciplinary analysis during optimization. After the multidisciplinary optimization system had been built, a bulb model turbine's runner was optimized using this system. After optimization, the Pareto solution was selected as the optimum solution. The optimum solution was then compared with the initial blade. The comparison results showed that after optimization, the efficiency of blade in optimum operating conditions had been improved 0.3%, and the maximum static stress on blade had been decreased 16.3%. The stress gradient on blade became more uniform, which showed that the optimum blade has better stress performance. In order to comprehensively compare the optimum blade with the initial, performance of initial and optimum blade in other conditions was also calculated and compared. The comparison showed that the optimum blade not only performs better in optimum conditions, but also performs better in other conditions. The comparison results verify that the idea of multidisciplinary optimization design of a hydro turbine runner is feasible, and the optimization system is effective.