Abstract: When constructing a sponge city in a collapsible loess region, the reinforcement of the loess roadbed needs to consider the permeability. In order to explore the roadbed fillers with higher strength and impermeability suitable for the construction of sponge city in loess area, this experimental study was performed to investigate the effect of polypropylene fibers in combination with cement and bentonite as a new stabilizer for improving the geotechnical properties of the loess. The Taguchi method was applied to the experiments and a standard L9 Orthogonal Array with four factors(Polypropylene fiber length, Polypropylene fiber content, cement content and bentonite content) and three levels were chosen. A series of unconfined compression and permeability tests were conducted on each specimen. And the signal-to-noise ratio analysis of orthogonal test and Taguchi method had obtained the optimal proportioning scheme for each mixing amount of improved loess. The results of these tests showed:that the most effective material for increasing the unconfined compressive strength of the samples was cement. Polypropylene fiber has the greatest influence on the permeability coefficient of the samples. Taking unconfined compressive strength and permeability coefficient as evaluation indexes, the optimum conditions for curing times of 3 days were Polypropylene fiber length(12 mm)、content(0.3%), cement content(8%) and bentonite content(3%). The optimum conditions test results were also superior in comparison with the lime-loess at 3, 7, and 14 days of curing time. The results of the study provide some reference for the subgrade treatment in sponge city road construction.