The intra-pulse spectroscopy based on a room-temperature distributed-feedback pulsed quantum cascade (QC) laser is introduced. The thermal chirp during a long excitation pulse is applied to a quantum-cascade laser centered at 7.85 [EQUATION]m, which is used for fast wavelength scanning. The laser spectra under different working parameters are compared and analyzed, with the aim of finding out the optimal working parameters of laser. The N[EQUATION]O absorption spectra centered at 1273.7 cm[EQUATION] are also obtained.