The codes for ejector nozzle with floating external adjustment sheet were specially developed, the flow field was numerically simulated by using parametric modeling method and grid partitioning technique. Turbulence model was selected according to predictions of explicit algebraic Reynolds stress, specific heat ratio (γ) was based on local temperature and gas compositions. The formulas of ideal nozzle parameters were derived using varied γ, which were used to analyze nozzle aerodynamic performance. The results obtained from constant and variable γ were compared. The results show that: nozzle mass flow rate is reduced because of more difficulty in airflow expansion, while nozzle thrust has a tiny change in variable γ cases. Moreover, the high temperature region of inner nozzle is larger and injected cold air is less despite of a smaller balanced floating sheet angle, which are detrimental to thermal protection.