In order to obtain the mechanism of laser ablation on the electrical properties of quartz fiber/epoxy wave-transmitting material under high density heat flux condition, we utilize continuous laser as heat loading source to carry out laser ablation, and test the dielectric constant of the material. The thermal damage evolution behaviors of quartz fiber/epoxy wave-transmitting material are obtained by the TG-DSC analysis of epoxy resin and quartz fiber. The infrared absorption spectrum and the crystalline material of ablation product on material after laser ablation are tested by transmission infrared spectroscopy and X ray diffraction, and the ablation morphology of the material is observed by scanning electron microscopy. The test results show that, after laser ablation at laser frequency of 7-17 GHz, the dielectric constant of the material dielectric constant is about 4.5, which is nearly 50% higher than before ablation. The laser irradiation makes the epoxy resin thermal decomposition and cracking, the graphite with conductive ability and chain state forms on material. At the same time, because of the rough and loose surface of the material, its reflection and scattering abilities on electromagnetic wave are enhanced, and the transmission capability is weakened.