Abstract: In this study,a sample of loess saturated with water at different depths in Taiyuan,Shanxi,was analyzed through a combination of mercury intrusion and scanning electron microscopy. The morphological characteristics of loess particles and pores were described,and the law of change with depth was revealed. The following conclusions are drawn:(1)Loess particles are affected by weathering,tending to refine with depth. (2)The stability of pores at different depths is related to multiple factors such as particle morphology and inter-particle cementation state. (3)The pores at different depths are divided into four size types:large(>20 μm),medium(5~20 μm),small(0.1~5 μm),and micro(<0.1 μm). The large pores are unstable and decrease with the increase of depth,while the micro pores are hardly affected by the depth of the soil. (4)In the range of medium and small pores,there are metastable pores of different sizes that can withstand a certain load beyond which they will collapse. The pores from large to small are gradually destroyed and transformed into smaller pores as the depth and pressure increase. The loess in this condition is still in a metastable structure and is collapsible. (5)When the depth increases until the weight of the soil exceeds the strength limit of the last metastable pores,the small pores are compressed and destroyed,and the loess structure tends to be stable. Below this depth,the loess almost loses its collapsibility.