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One of infrared remote sensing instruments carried by FY-4 meteorology satellite is a space-borne Fourier Transform Spectrometer (SBFTS). It acquires temperature, pressure and humidity of atmosphere on geostationary orbit, and supplies the valuable weather data for future numerical weather prediction. It uses a 16x4 plane array rectangular detector, so it can measure the spectra and spatial image simultaneously. The maximum optical path difference of the SBFTS is 0.8cm. Objective: This paper's mainly analyses the three factors (maximum optical path difference, off axes detectors, the tilt angle of the moving mirror) that influence spectral resolution of SBFTS and convinces through experiment. Methods: First, the three primary factors that will influence the instrument line shape (ILS) are discussed here. The ILS is deduced when the three factors are taken into account separately. The final function of ILS is the convolution of the three parts. And the spectral resolution is the half width of the ILS. The gases NH3 and CO are used to detect the ILS of the instrument in the long wave band and middle wave band separately. Their absorption line shape is Lorentz distribution in atmospheric pressure and room temperature. Now the absorption line shape of the gases and the ILS are given. They can be combined to the instrument detecting line shape theoretically. Finally it is compared with the line shape that is really detected by the instrument using gas cell methodology. The lines almost have the same shape and width. Results: The spectral resolution of SBFTS is presented leave each other in theory and experiment. The results are according to each other. Conclusion: The spectral resolution of SBFTS mainly lies on the maximum optical path difference. The interferogram is referred to as being "auto-apodized" since the off-axis effect and tilt angle of the moving mirror theirself appear to impose an apodization function on the interferogram. The auto-apodization of the interferogram is likely to result in a ILS that is broadened in frequency and reduced in amplitude. In addition, the ILS appears to be shifted in frequency and the side-lobes of the ILS are asymmetric. In the long wave band the spectral resolution of SBFTS only rest with the maximum optical path difference. It is not infected by off axes effect because of using plane array detectors and the small tilt angle of the moving mirror. But in the middle wave band its spectral resolution is debased by the off axes effect.
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