Much high frequent light exist in the near-field of the high energy chemical oxygen iodine laser (COIL), which cause serious harm to beam quality and system near the high power beam tune. So it is necessary to study the propagation laws of the high frequency light. The generating mechanism and characteristics of different high frequent light are analyzed. Since the diffraction of cavity mirror and higher-order modes contribute to most of the high frequent light, they are main objects of the study. The energies of different positions are measured by the measurement diaphragm set in the beam tune. The angular power spectra of the high frequent light are calculated according to the corresponding space angles on the diaphragm. The angular power spectrum curves changing with the duration are analyzed by three different methods, and the accordant results are got. The research results show that the angular power spectrum in the front is bigger than that in the back, and the angular power spectrum increases with the deterioration of beam quality, and in the same time, the energy loss may enhance, too. The power and energy on each defending diaphragm can be calculated with the angular power spectra, which lays a good foundation of heat control technology for the high energy COIL.