Abstract: To address the insufficient understanding of the mechanical substitutability of transparent sand for natural sand under high-relative-density conditions, transparent sand composed of fused quartz sand with a particle size of 1～3 mm and a 60% calcium bromide solution was prepared in this study. At a relative density of 85%, permeability tests, one-dimensional compression tests, direct shear tests and triaxial tests, were conducted to compare the mechanical properties of transparent sand and saturated natural sand. The results indicate that the two materials are of the same order of magnitude in terms of permeability coefficient, compression modulus, and shear strength parameters. The increase in pore fluid viscosity slightly reduces permeability and strength, while having limited influence on deformation characteristics and dilatancy behavior. Comprehensive analysis demonstrates that the transparent sand system achieves a favorable balance between refractive index matching and mechanical similarity. Under the specified conditions, it can accurately simulate the mechanical behavior of saturated natural sand, making it suitable for visualization model tests of soil–structure interaction in geotechnical engineering applications such as foundations and embankments.