In order to obtain the microscopic characteristics inside the lightning channel, a lightning dual band optical observation system is designed. The system mainly consists of a signal capture module, a signal reception and conditioning module, a signal acquisition module, and a power supply module. The transmission coefficient of the system can be calibrated by using a standard light source. The system can directly observe the time-domain full wave waveforms of different wavelength optical signals, and can analyze the temperature and conductivity information of channels through relative spectral line intensity. Based on the similarity between gap discharge and lightning, the designed system is employed to observe the gap discharge channel, and the temperature and conductivity of the gap discharge channel are calculated. The results indicate that the temperature variation range of the gap discharge channel in this experiment is 5 400~5 980 K, and the conductivity variation range is 10.93~28.53 S/m.