The tunable diode laser absorption spectroscopy under a pulse wavelength scan scheme is adapted to home-made room-temperature mid-infrared distributed feedback quantum cascade lasers; and identification of N2 O spectral fingerprint is demonstrated experimentally. By driving the laser at 800ns pulse duration, a wave number tuning of about 1.6 cm- 1 is produced, which make both 1289.04 cm- 1 and 1289.86 cm- 1 absorption fingerprints of N2 O gas to be definitely assigned. The measured relative absorption intensity is consistent with the HITRAN data precisely.