Abstract: The coarse-grained soil is widely used in earth-rock dams and road projects. Its seepage characteristics are related to the stability and safety of the projects. The permeability coefficient is the basic parameter of seepage characteristics, and the gradation is the key factor affecting seepage. In order to study the effect of gradation on the permeability coefficient of the coarse-grained soil, based on the results of permeability tests in the existing literatures, a continuous gradation equation is used to describe the gradation of quantitatively graded coarse-grained soil, the relationship between the gradation and the permeability coefficient is studied, and an empirical formula for the permeability coefficient considering the area of gradation curve is established, and other literatures are used to study the relationship between the gradation and the permeability coefficient. The results show that the gradation curve of graded continuous coarse-grained soil can be quantitatively described by the continuous gradation equation, and the empirical formula for the permeability coefficient based on gradation area can be applied to the coarse-grained soil with different maximum particle sizes and gradations.