According to the floating weight balance characteristics and the ideal gas state equation, a method to control the height of the aerostat′s flat flight by gas mixing was explored, and the overall design research of constant-height flight by air-lifting gas mixing was carried out. Considering the importance of thermodynamic characteristics to the ascent process and the flat flight process of the aerostat, combined with the thermophysical properties of mixed gas in engineering thermodynamics, the super-pressure balloon was taken as the research object to analyze the thermal environment during the ascent and flight processes of spheres, and coupled with dynamic models. On this basis, the mechanical simulation of the ascent and flat flight process of the balloon was carried out, and the changes in altitude, speed, gas temperature and pressure during the ascent of the balloon were obtained, so as to verify the feasibility of the theoretical model of constant-height flight by air-lifting gas mixing, and provide guidance for the subsequent aerostat flight test.