Abstract: The main circulation pump is an important component in nuclear power plant, whose weight and volume are the important influence factors on the overall weight, volume and the arrangement of nuclear power plant. The optimization design of the weight and volume for main circulation pump was carried out based on a complex-genetic algorithm, which was a self-developed method. The optimal weight and the optimal volume are 10.82% and 4.28% less than that of the referenced pump, respectively. It can be seen that the optimization effect is obvious. The effects of operation parameters of primary loop and rotating speed of pump on the weight and volume for main circulation pump were also analyzed. Corresponding results can provide reference for engineering design.