Abstract: Attenuation characteristics of High Power Microwave (HPM) with different frequencies (L, S, C, X band) penetrating through reinforcement nets were studied by simulation tests combined with the finite-difference time-domain method in this paper. The research models reflect various kind of reinforcement nets with different diameters, different meshes, different spacings between layers, and different arrangement. The results show that shielding effectiveness of reinforcement nets against HPM exists. And shielding effectiveness is better when the mesh is smaller than half of the wave-length, or when the spacing between layers is odd number times a quarter of the wave-length, or when the reinforcement nets are arrange is stagger. The reinforcement nets with dissimilar forms can be comprehensively utilized in protective constructions for the best result.