Laser ablation emission spectra of graphite/potassium nitrate under pulse laser irradiation with wavelength of 1064 nm are analyzed to investigate the chemical reaction processes during laser ignition. Testing results indicate that ablation spectra possess the characteristics of line spectra, and wavelengths of spectra range mainly from 300 to 600 nm. Ablation spectra mainly consist of atomic spectrum and ionic spectrum of N, O, C and K. When the laser energy density is 46.7 J/cm2, NⅡ385.61 nm spectrum is the strongest while OⅡ441.70 nm spectrum is the weakest. The ablation products combusted in gas phase.