Abstract: To satisfy the demand of spongy city road construction in collapsible loess areas, a kind of cotton stalk fiber EPS particle light soil with light weight, high strength, and certain permeability was developed as a roadbed replacement material. This lightweight soil is a mixture of cotton straw fibers, polystyrene (EPS) granules, cement, loess, and water. In the present study, the density, strength, deformation and permeability of lightweight soil with different cotton stalk fiber contents and lengths, different EPS particle contents and particle sizes, and different cement contents were tested by a series of geotechnical tests. The mixture ratio of cotton stalk fiber EPS particle lightweight soil was designed. The results show that among the various components of lightweight soil, the content of EPS and cement content have the most significant effect on the density. Besides, there is a positive correlation between cement content and strength, and a negative correlation with the permeability coefficient. The EPS content and particle size are negatively correlated with the strength of the lightweight soil, and positively correlated with the permeability coefficient; the addition of cotton stalk fiber improves the plasticity of the lightweight soil and improves the permeability of lightweight soil to a certain extent. The order of magnitude of the effect of various factors on the strength of lightweight soil is: cement content>EPS content and particle size>cotton stalk fiber content and length. The optimal mix ratio of lightweight soil to satisfy the demand of spongy city road construction in collapsible loess areas is: loess soil∶cotton stalk fiber (length 9 mm)∶EPS particles (particle size 0.5-1.0 mm)∶cement∶water = 1,000∶4∶18∶35∶400.