Abstract: The electronically excited CH radicals were produced by photodissociation of CHBr₃ molecule using quadrupoled YAG laser. The dispersion spectroscopy of CH（A,B→X）, the time-resolved spectroscopy of CH（A→X） at 4315Å, the dependence of the signal intensity of CH（A→X） at 4315Å on energy density of laser were measured. According to these measurements, the mechanism of the photodissociation of CHBr₃ molecule is proposed. CHBr₃ molecule absorbs continuously three single 266nm photons （i.e. 1+1+1 photon absorption process）. By measuring the dispersion spectroscopies of CH（A→X） at different delay time refer to laser firing time, the rotational relaxation process of CH（A） radical was investigated. It is found that the rotational relaxation of CH（A） is nearly finished in present experimental conditions, i.e. 26.6 Torr of total pressure of Ar and 15 mToor of CHBr₃ within 100 ns duration.