Abstract: In order to improve the power generation efficiency and protect the gas generator set, it is necessary to separate the liquid water in the gas before the gas enters the generator set. Firstly, this paper analyzes the advantages and disadvantages of different gas-liquid separation mechanisms, and designs a vertical gas-liquid separation device combining gravity and screen filtration. Then, the diameter design of vertical gas-liquid separation device was carried out based on the fact that the gas rising velocity in the gas phase space was equal to 80% of the droplet settling velocity. Then the screen of the gas-liquid separation device was selected. Finally, the height of the device is designed.The gas-liquid separation device is designed according to the working parameters of the DN500mm gas transmission pipeline in Shanxi lanneng power station. The calculation shows that the diameter of the gas-liquid separation device is 1.3m; SP type wire mesh demister with nominal diameter of 1.1m shall be selected for wire mesh; The total height of the gas-liquid separation unit is 2.92m.