Abstract: Using the methods such as infiltrating water experiment,total porosity,measurement of susceptibility and magnetic susceptibility, we did some research on the permeability of S₁-L₄ layers in the Changwu loess section and on its mechanism of formation. The research result shows that the infiltration rate of the loess and red-brown paleosol layers changed greatly.During the first 20 minutes,the change was extreme and we called it an enormous change stage. In about twenty minutes the infiltration rate changed less than before and we called it a gradual change stage.The infiltration rate of the loess is larger than the red-brown paleosol layers.For example,the steady infiltration rate of loess layers is 2.01 mm/min and that of red-brown paleosol layers is 0.71 mm/min. Porosity and moisture space of the loess layers are also larger than those of red-brown paleosol layers,so the loess layers can form water-bearing layers more easily than the red-brown paleosol ones and the latter can form water-resistant layers more easily than the former. The red-brown paleosol layers have definite permeability and the nature of water-resistance is stronger than that of the loess layers. It is the reason why the groundwater of loess has many layers. The susceptibility of loess layers is lower while that of the red-brown paleosol layers is higher, which shows that the difference between the red-brown paleosol layers and loess layers in permeability was mostly determined by climate changes during ice age and interglacial stage. The result showed that conditions and laws of enrichment of the loess groundwater were controlled by climate changes during Quaternary. This has an important application value to development and utilization of loess water resources.