Decomposition process of benzene in a low pressure DC glow discharge in pure benzene and nitrogen-benzene mixture is investigated by emission spectroscopy, gas detection tube and infrared absorption spectroscopy. In the pure benzene discharge, the emission spectra of benzene are seen at the beginning, and they decrease, then the emission spectra of CH(431.42nm), C₂(468.02nm, 516.52nm), H_α(656.28nm) and H_β(486.13nm), which are regarded as the fragments of benzene, are observed, so that it is judged that benzene is decomposed by electron impact in the DC glow discharge. In the nitrogen-benzene mixture discharge, the emission spectra of CN(787.27, 918.95nm, etc.) are observed with those of the fragments of benzene and those of nitrogen excited molecules and ions. The emission intensity of CH reaches its maximum first, then the emission intensity of H_α and CN reach their maxima. Therefore, it is likely that benzene is decomposed into CH and other by-product first, then H and CN is created. It is found that the temporal variation of the emission intensity ratio of the first negative (0, 0) band to the second positive (0, 0) band of nitrogen ions and excited molecules, which infers electron mean energy, qualitatively agrees well with that of the decomposition rate of benzene.