<p>This study presents a novel method for visualizing the internal structure of soil using transparent soil technology combined with planar laser-induced fluorescence technology. Fused quartz sand was employed as soil particles, while mineral oil served as the fluid. Permeability experiments were performed to capture two-dimensional images of the soil's internal structure. Six filtering methods were assessed for image processing, and the comparative analysis identified the Laplacian method as the most effective in differentiating particles from pores and accurately predicting soil porosity. Using Particle Image Velocimetry (PIV), the maximum flow path length of fluid at the soil-structure interface was found to be 6–7 times the average particle diameter, whereas flow paths within the soil were restricted to 1–2 times the particle diameter. The study also revealed that while PIV technology is effective for measuring soil porosity, the accuracy of the results is highly dependent on grid size, with excessively large or small grids introducing significant measurement errors. By analyzing two-dimensional slices, a three-dimensional soil model was developed, enabling detailed visualization of the soil's internal structure. Experimental findings showed that the number and volume of non-connected high-velocity flow paths decreased inversely with the relative density of the soil. This research provides an innovative approach and technical framework for observing and analyzing internal soil structures, offering valuable insights and practical support for geotechnical engineering applications.</p>