The invention discloses a small reflective off-axis 
telemetry calibration 
system for an FTIR front end. The small reflective off-axis 
telemetry calibration 
system comprises a diaphragm, a first off-axis parabolic mirror, a 
plane mirror, a second off-axis parabolic mirror, a third off-axis parabolic mirror, a 
black body, an FTIR 
spectrometer, a vertical turntable bearing, a lens cone, a top cover and a horizontal turntable bearing. The off-axis reflection type telescopic light path is adopted, compared with a common cassette 
telescope for FTIR 
telemetry, aperture blocking does not exist, the energy 
utilization rate is higher, and the 
detection limit of passive telemetry can be effectively improved; spatial 
layout is adopted, only the 
telescope objective is required to rotate and 
pitch when the instrument is used for 360-degree horizontal and 60-degree 
pitch scanning, the scanning is flexible, and the speed is high; the FTIR 
spectrometer is kept still, and the measurement stability is better; the size and the weight are reduced, the 
shock resistance is improved, and the 
system is better applied to vehicle-mounted and airborne conditions; the telescopic 
optical path and the 
black body calibration 
optical path are carried out in a time-sharing manner, and the off-axis design is adopted, so that the energy 
utilization rate of passive remote measurement can be effectively improved.