As a type of reliable renewable energy, tidal energy has great potential for development. But its technology is behind other renewable energy sources. One of the constraints is the efficiency and stability of tidal turbine. The objective of the present work is to optimize a rim-generator turbine runner by improving hydraulic performance and stress level. A multi-objective optimization based on the response surface methodology is adopted during the optimization process so that an optimal runner blade can be identified. Both the blade shape and the number of the blade are determined. The numerical method is verified by comparing with the experimental test, and the numerical results show good agreement with the experimental results. The hydraulic losses in the ebb generation mode and the flood generation mode are compared, and the mechanism of the difference of the hydraulic losses between the two modes are analyzed, especially the hydraulic losses in the guide vanes. The stress analysis based on the fluid-structure interaction theory shows the optimized rim-generator turbine runner has good structural strength. This work could contribute to the development of the rim-generator turbine, and further to the utilization of the tidal energy.