Abstract: Loess is inherently water-sensitive and highly porous, resulting in poor resistance to water and gas permeation and making it susceptible to structural deformation and geological hazards such as collapses and landslides. Cement improved loess (CIL), characterized by high density can compensate for the poor water and gas seepage resistance of loess. However, the patterns and mechanisms of its water and gas permeability remain unclear. In this study, CIL was investigated through laboratory water permeability tests, air permeability tests, and scanning electron microscopy (SEM) observations. Specimens with varying cement contents and curing ages were prepared to systematically examine the effects of cement dosage and curing time on water and gas permeability characteristics. The results show that with an increase in cement content, the permeability coefficient and air permeation rate of CIL decrease progressively, indicating a significant reduction within the 0~8% cement content range. This decrease follows to a power function relationship. As the curing age increases, the permeability coefficient and air permeation rate of CIL decrease correspondingly. A double-logarithmic linear relationship is observed between the permeability coefficient and the air permeability, suggesting that one parameter can be reliably predicted from the other. From a microscopic perspective, cement changes the internal structure of loess by filling pores, cementing aggregates, and surface attachment, leading to differences in water and gas permeability. These findings can provide a theoretical basis for the problems of water and gas permeation in loess and the application of CIL in engineering.