Abstract: In order to gain quickly the quantity of the drain of the nuclear power plant steam pipe, by calculating the quantity of the drain of the steam pipe in the start period and normal operation period, the heat dissipation picture of steam pipes with various piping specification are analyzed and drawn. By the heat dissipation picture, the quantity of the drain of the steam pipe in nuclear power plant can be obtained quickly when selecting the steam traps. To extend the life and reduce the cost of traps, this paper analyzes the influence of trap’s different safety factors (k) on its performance, and it recommends the suitable safety factor of traps used in the steam pipe of the nuclear power plant. It can improve the utilization efficiency of steam and economic benefits, and prolong the life of traps and reduce the cost of manufacturing of traps.