Abstract: The electromagnetic radiation produced by the resonance of the target chamber is one of the sources of electromagnetic pulse generated in the experiment of ultra-short intense laser and target interaction. Based on the finite element analysis method, we simulated the two processes of the electromagnetic pulse produced by the resonance of cavity and electromagnetic pulse propagating outward through windows. The former results show that the internal structure has a significant influence on the intensity distribution and resonance frequency of the electromagnetic field. The latter simulation results show that the electric field intensity outside the window is about 40% higher than that inside the window, and the electromagnetic pulse propagates to the target outside and then spreads and attenuates in the form of spherical wave form. The intensity attenuation rule is analyzed and the fitting function of the attenuation curve is obtained.