The purpose of this paper is to investigate the 3D reconstruction and seepage simulation of vermiculite-based sealing materials in order to clarify the relationship between material structure and fluid leakage in order to improve their performance and reliability and to provide a foundation for accurate leakage rate calculation under various conditions. CT scanning and 3D reconstruction techniques were used to examine the pore structure and fractal properties of vermiculite-based sealing materials. The seepage mechanism under compression was examined using a porous medium model. The findings demonstrate that the vermiculite-based sealing materials have self-similarity and scale-invariant fractal properties. The porous media model in compression exhibits a low leakage rate, opening up a new avenue for realizing microscopic leakage studies with a leakage rate of 1 × 109 in compression.