Abstract: Permeability and collapsibility are important indicators reflecting the engineering properties of loess. Analyzing the relationship between collapsibility and permeability from a microscopic perspective is a key content in the study of loess engineering stability. Taking the sandy loess in Jingbian County, northern Shaanxi as the research object, this paper uses collapsibility tests, permeability tests, scanning electron microscope (SEM) analysis and other methods to study the collapsibility and permeability deformation characteristics of sandy loess and the microscopic mechanism of their mutual influence. The results show that: (1) The sandy loess is a moderately collapsible soil, and its collapsible deformation first increases and then decreases with the increase of axial pressure, and the collapsible deformation is greater at low water content. (2) The permeability coefficient of sandy loess gradually decreases with the increase of water content, and it decreases significantly after collapse. (3) The average pore diameter of the collapsed soil decreases, while the average pore diameter increases under seepage, and the repeated seepage after collapse can lead to an increase in the average pore diameter of the soil. (4) Under the action of collapse, the clay particles on the surface of loess particles are destroyed by water, and the particles are rearranged to produce collapse deformation; the number of interconnected pores between particles increases under the action of seepage water pressure; when the collapsed soil sample is subjected to seepage water pressure again, the clay particles attached between particles are lost and block the seepage channel, which is the internal reason for the influence of collapse on seepage. The research results have important guiding significance for revealing the essence of loess collapsibility and engineering stability research.