<p>The deformation and structural damage of loess during water penetration directly or indirectly cause numerous geological and engineering disasters in collapsible loess areas. Thus, it is crucial to analyze the effect of permeability on loess collapsibility. This study focuses on the collapsible Q₃ Malan loess. A custom-made measuring device was used to determine the saturated permeability coefficient <i>k</i>_<i>w</i> and air permeability <i>k</i>_<i>a</i> of loess before and after collapse. A quantitative mapping relationship between the void ratio, the permeability coefficient, and the gas permeability rate was established. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the effect of permeability on loess collapse at the microscopic level. The results indicated that loess collapse reduced permeability. The saturated hydraulic conductivity was 4 to 5 times lower, and the gas permeability was nearly one order of magnitude lower after the collapse than before. The saturated hydraulic conductivity (<i>k</i>_<i>w</i>) and air permeability (<i>k</i>_<i>a</i>) exhibits a linear logarithmic relationship with the void ratio (φ) before and after collapse. At the same void ratio, the hydraulic conductivity and air permeability was lower after the collapse than before. Collapse events reduced the pore volume and permeability by altering pore morphology, reducing pore connectivity, and decreasing the number of effective seepage pathways. The swelling and dispersion of clay minerals in the presence of water, as well as the accumulation of fine particles in pore channels, blocked fluid migration paths. This study provides a reference for seepage control, foundation treatment, and geological disaster prevention and control in construction areas in loess regions.</p>