In order to study the B2Σ+~X2Σ+ spectra of CN radical and temperature under different conditions, laser-induced breakdown spectroscopy was used to break high purity graphite in air environment and produce CN free radicals. Emission spectra of B2Σ+~X2Σ+ were measured by high resolution spectrometer. The spectra of CN radicals under different conditions were studied by changing laser energy and laser focus position. The results show that, when laser energy is tuned from 30mJ to 50mJ and the increasing step size is 5mJ, spectral intensity increases with the increase of laser energy. When single pulse energy is 50mJ, spectral intensity reaches its maximum. In addition, when the distance between the upper surface of graphite and laser focal point is 8mm, signal-to-noise ratio reaches the maximum. LIFBASE software is used to fit the spectral data. The vibration temperature of CN radical is about 104K. The rotating temperature is about 4000K. Vibration temperature of CN radicals decreases and rotational temperature increases with the increase of distance. These results play an important role in studying cosmic stars and exploring high temperature chemical reaction.