An Observing System Simulation Experiment (OSSEs) for the National Polar-Orbiting Operational Environmental Satellite System (NPOESS) is underway to provide guidance for NPOESS instrument configuration. In OSSEs, the forecast impact of an instrument can be assessed by adding or removing simulation observation in the analysis. The ECMWF reanalysis and free forecast integration in February 1993 has been provided as a 'true' atmosphere from which simulations can be computed. AIRS is considered to be a high spectrum resolution infrared sounder which will act as a prototype for NPOESS. AIRS measures radiance in the 3.7µm to 15.4µm spectral region and has 2378 channels to retrieve atmospheric properties such as water vapor and temperature profiles. The simulation radiances of AIRS are generated with fast radiative transfer model. The simulation observation data will be assimilated by the NCEP analysis system to test its impact.