In order to study the heat transfer performance of vapor condenser with flat finned tube, an experimental system of vacuum cooling vapor condenser is designed and its heat transfer performance is tested. The system runs for about 450 s, the simulated heat source temperature in the vacuum chamber drops from 80 ℃ to 25 ℃, and the condensed water is about 2.9 kg. The experimental results show that the higher the evaporation power is, the more intense the water evaporation is. The peak cooling capacity of condensate steam in the water catcher is 45.0 kW, the peak heat transfer coefficient is about 53.68 W/(m²·K), and the average heat transfer coefficient is 38.34 W/(m²·K). Compared with the vapor condenser with smooth tube, the cooling time of vapor condenser with flat finned tube is shortened by 17% and the quality of condensed water is improved by 7.41%.