An analysis model is established and a theoretical formula is deduced to analyze the electromagnetic shielding enhanced by a double-layer micro-nano structure. By using the square structure as an example， the effectiveness of the electromagnetic shielding enhanced by the double-layer micro-nano structure is investigated， and a calculation formula for the electromagnetic shielding of the double-layer structure is derived. In addition， a full-wave simulation is carried out using CST Microwave Studio， the results of which are in good agreement with those of the theoretical calculations. In the full-wave simulation， the micro-nano structure is two-three orders of magnitude smaller than the calculated corresponding wavelength， which verifies the correctness of the mechanism analysis and the calculation of the full-wave simulation software. The analysis of the electromagnetic shielding enhancement mechanism and the provided calculation formula can be extended to the multilayer micro-nano structure， which is universal. To further verify the accuracy of the mechanism analysis and the full-wave software simulation results， a square double-layer micro-nano structure sample is prepared. The measured results of the sample are essentially consistent with the theoretical and full-wave simulation results. The shielding effectiveness is greater than 45 dB in the range of 2-18 GHz， and the average light transmittance exceeds 71%， which has good transparent shielding performance. This mechanism analysis provides theoretical guidance for designing micro-nano structures with increased light transmission and high-efficiency electromagnetic shielding performance.