A theoretical model of scattering from three-dimensional arbitrary layered media with 3D infinite rough surfaces based on the small perturbation method (SPM) is derived in the present paper. The scattering field and bistatic scattering coefficient for linear polarized waves are derived respectively. Firstly, the electric and magnetic fields in each region of the layered structure are expanded into perturbation series in spectral domain. Secondly, the expansion coefficients of each order are obtained by applying the boundary conditions. As a result, the expressions of the zeroth-, firstand second-order solutions of the scattering problem based on the SPM are obtained, in which the second-order solution is the primary contribution of this work. The theoretical model is helpful to understand the dependence between the scattering field and physical properties of the layered structure (such as surface roughness and dielectric constants at different depths). The result can be applied to modeling of the received radar signal from nature targets such as layered soil and ice with full polarizations.