Wrinkles of a stiff thin layer attached on a soft substrate have been widely observed in nature and these phenomena have raised considerable interests for several decades.The underlying mechanism of wrinkling is generally understood as a stress-driven instability.In terms of stability study, several theoretical works have been devoted from linear perturbation analysis to nonlinear analysis.Most previous studies have been mainly constrained to consider a homogeneous substrate, to determine the critical condition of instability and the corresponding wrinkling patterns.Nevertheless, many practical systems have a functionally graded substrate.For instance, the deposition process of a stiff thin film on a soft substrate may lead to the variation of the mechanical properties of the substrate along the thickness direction (functionally graded), which would effect the wrinkling of film/substrate system.The buckling and post-buckling of surface wrinkles with functionally graded substrate are only recently being pursued [1-2].