Sensitivity is an important radiation performance index of remote sensor. In this paper， the sensitivity concept of infrared hyper-spectral sounding is extended from the sounder noise sensitivity to the atmospheric parameter sensitivity and the surface temperature error sensitivity for the on-orbit application of sounder. The corresponding sensitivity calculation models and their relations are introduced. These models are applied to the sensitivity evaluation of the first infrared hyper-spectral atmospheric sounder on geostationary meteorological satellite FY-4A GIIRS. With the sounder test data and the atmospheric historical statistical data， we obtained the quantitative variation characteristics of the atmospheric parameter sensitivities （atmospheric temperature， water vapor， ozone， CO₂， CH₄ and N₂O）， the surface temperature error sensitivity and the sounder noise sensitivity with the channel. The physical mechanisms of these characteristics are analyzed. The results show that， as a whole， the sensitivities of atmospheric temperature， water vapor and ozone are much higher than that of the sounder noise and surface temperature error， while the sensitivities of CO₂， CH₄ and N₂O are submerged by the sounder noise sensitivity and the surface temperature error sensitivity. The study lays a foundation for the signal-to-noise ratio evaluation of infrared hyper-spectral atmospheric parameters detection， and is helpful for the optimization of infrared hyper-spectral atmospheric sounding channels.