With a well-developed infrared radiation transfer model KCARTA,the effects of spectral resolution,spectral response function shape,spectral calibration accuracy,propagation path and surface emissivity on the detected brightness temperature for hyperspectral sounding were simulated.The results from forward simulation show: 1) improvement of spectral resolution will increase detectable brightness temperature 2) any uncertainties from internal and external factors will lead up to much larger brightness temperature difference for hyperspectral sensor than for low spectral sensor.Results can be taken as the referrence in designing future hyperspectral IR sensors and in developing hyperspectral retrieval algorithm.