Abstract: The volumetric deformation and particle breakage of crushed stone soil under high stress will alter its permeability. To investigate the changes in the permeability of crushed stone materials before and after particle breakge under confined pressure, a large-scale permeameter with an independently controllable axial loading system is designed to conduct seepage tests on the crushed stone soil under pressures. The permeability characteristics of crushed stone soil under confined pressure are obtained, and the relationships are established among permeability characteristics, pore ratio, gradation and axial pressure. The results indicate that as the axial pressure increases, particle breakage intensifies, leading to an increase in the content of fine particles and a decrease in the porosity, resulting in a significant reduction in seepage velocity. When the crushed stone soil experiences seepage within a small range of hydraulic gradients, there is a generally linear relationship between hydraulic gradient and flow velocity. The stress state has a significant impact on the permeability characteristics of the crushed stone soil, with a notable decrease in the permeability as the axial pressure increases.