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.