The invention discloses a small reflective off-axis telemetry calibration system for FTIR front end, comprising a window plate, a first off-axis parabolic reflector, a plane reflector, a second off-axis parabolic reflector, and a third off-axis parabolic reflector mirror, black body, FTIR spectrometer, vertical turntable bearing, mirror tube, top cover and horizontal turntable bearing. The present invention adopts the off-axis reflective telescopic optical path, and compared with the cassette telescope commonly used in FTIR telemetry, there is no aperture obstruction, and the energy utilization rate is higher, which can effectively improve the detection limit of passive telemetry; the spatial layout is adopted, and the instrument is 360° horizontal , When scanning at 60° pitch, only the telescopic objective lens needs to be rotated and pitched, and the scanning is flexible and fast; the FTIR spectrometer remains stationary, and the measurement stability is better; the volume and weight are reduced, the shock resistance is improved, and it is more practical for vehicles , Airborne; the telephoto optical path and the black body calibration optical path are carried out in time, and the off-axis design adopted can effectively improve the energy utilization rate of passive telemetry.