Cemented sand gravel (CSG) is an environmentally friendly dam construction material. Its permeability performance under loading is crucial for engineering applications. This study investigates the permeability of CSG under axial compression through laboratory experiments. Four mix proportions of CSG specimens were tested under 10–60 % of ultimate compression strength. Permeability test, ultrasonic monitoring, and nuclear magnetic resonance (NMR) techniques were utilized to analyze the permeability coefficient, damage, porosity, and pore size distribution. Results show the permeability coefficient increases with loading level, following a quadratic polynomial relationship with porosity and damage (R2>0.98). NMR tests reveal reduced micropores and increased small, medium, and large pores. Damage value defined by ultrasonic wave velocity increases with loading, with higher value in vertical than loading direction. Grey relational analysis identifies medium and large pores have high impacts on permeability. A regression model based on pore size distribution effectively predicts the permeability coefficient (R2=0.88). This study reveals the deterioration of CSG under axial loading and the relationship between microstructure and permeability coefficient. The findings can guide the seepage control design of CSG dams.