This article conducts optimization and sensitivity analysis for the cold-end system of a nuclear power plant (NPP) with a sea water circulating system, using the minimum annual cost method by dynamic economical analysis. The following factors are taken into account for the optimization: the design of a condenser (cooling area and the parameters of cooling tubes), the scale of the cooling tower, the flow rate of circulation water, and the diameter of circulating pipes. In conclusion, the optimum scheme of the cold-end system is obtained for the double-back pressure turbine project. The variation trend of the annual cost with changing circulating water amount is also concluded. Finally, this article provides the sensitivity analysis of the feed-in tariff.