The process of development of steam condenser for steam-gas mixture has been described. The construction is based on idea to maintain a constant steam-gas mixture speed along the steam condensation channel. The shape of the channel with constant speed is described. To research the heat-mass transfer of gas- steam mixture the test plant with tubes dissected by thermocouples, have been realized. In the process of testing there where changes of gas- steam mixture speed, pressure and air concentration from 0% to 18%. The experimental results have been summarized by dimensionless equation. The pressure drop and increase of air concentration also contributes to the decrease in a saturation temperature. So there Is optimal speed when the surface area of channel in condenser will be minimal. The optimal speed value is about 30 – 50 m/s. The research results are implemented in the experimental model of high-efficiency condenser. The heat transfer coefficient in this model is equal about 4500 – 2700 W/(m2K), if the air concentration at inlet is 0–8 %. The design of high-efficiency condenser for gas-steam turbine plant 25 MW capacity and condenser with vertical tubes have been presented.