Abstract: Inorganic curing agent modified loess is often used as roadbed filler in road construction projects in Northwest China. Under the climatic conditions of large temperature difference in Northwest China, improving the strength of loess and reduce the freeze-thaw deterioration of anti-seepage performance of roadbed soil is of great significance to the safe service of roadbed. At present, the research on the improved loess pays more attention to its mechanical properties and the freeze-thaw stability of the anti-seepage performance of the improved soil is relatively scarce. This study proposed a new method based on the combination of reinforced soil mechanics and conventional improvement methods-fiber material-curing agent to improve loess and then analyzed its permeability stability under the influence of freeze-thaw cycles. Based on the unconfined compressive strength test, the optimal fiber length and the optimal content of cement and fiber were determined. The permeability analysis of fiber reinforced soil, cement soil, and cement-fiber improved soil was carried out through triaxial permeability test and microscopic test. The results show that under the unconfined compressive strength test, the effect of adding polypropylene fiber with a length of 12 mm into loess is the best, and the optimal dosage of cement and polypropylene fiber is 2% and 0.3% respectively. In the study of the permeability coefficient of fiber reinforced soil, it is found that the confining pressure will inhibit the water conductivity of the fiber, so that the permeability coefficient of the reinforced soil decreases first and then increases with the increase of the fiber content. The permeability of cement-fiber loess is affected by many factors. Under low cement content, the permeability coefficient decreases first and then increases with the increase of fiber content. When the cement content is 5 %, the permeability coefficient decreases with the increase of fiber content, and cement is the main factor affecting the permeability of cement-fiber modified loess. The permeability test and nuclear magnetic resonance test of different soil samples under freeze-thaw condition show that the increase of permeability coefficient and porosity of cement-fiber modified loess under freeze-thaw effect is the smallest; thus, the cement-fiber modified loess has better freeze-thaw stability. The research results can provide theoretical support for the optimization of loess improvement technology in the seasonal frozen area.