Abstract: The condenser is one of the most important equipments in nuclear power plant secondary loop, whose weight and dimension influence the weight, volume and arrangement of nuclear power plant. The mathematical model for condenser simulation was established by using empirical heat transfer formula and condenser industrial test results, which included thermal power balance calculation, resistance calculation, vibration analysis, condenser weight and condenser volume calculation. The corresponding computer code was programmed to verify the accuracy of the model. The sensitivities of cooling pipe outer diameter, cooling pipe pitch and the flow rate of cooling water, which influence the weight and volume of the condenser, were analyzed. The condenser weight and volume were optimized by improved genetic algorithm. The results show that condenser weight obtained with the optimal scheme is 6.926% less than the original, the volume is 12.587% less than the original, and the optimal effect is significant.