Abstract: Taking two typical F-class gas-steam combined cycle units of GE 9FA and Mitsubishi M701F as the research objects, a thermal model of gas-steam combined cycle with inlet gas heating design was established, and a simulation calculation for the thermal performance of unit was carried out. A univariate analysis was conducted on the effects of the environmental temperature, heating temperature rise, and unit load on the unit performance, while a comparative analysis was conducted on the improvement of inlet gas heating efficiencies of two types of units under different unit loads. After which, the optimal intake parameters under different unit loads were given. Results show that, under the same inlet gas heating condition, the efficiency improvement of 9FA unit is higher than that of M701F unit, and the unit combined cycle efficiency increases with the increase of heating temperature rise. Under the same heating temperature rise condition, the optimal environmental temperature for inlet gas of 9FA unit is higher than that of M701F unit. Research results have important reference significance for the application of inlet gas heating technology in F-class gas-steam combined cycle units.