In this paper, let E denote the attrator of an iterated function system (X,T1,…, Tm). One can define a continuous self-mapping f : E→E by f(x)=T-1j(x), x∈ Tj(E), j=1, …, m . Given ψ ∈CR(E), let
Kψ(δ, n = sup{∣∑n-1k=0[ψ(f kx)-ψ(f ky)]|:y ∈ Bx (δ, n)},
where Bx(δ, n) denotes the Bowen ball. Choosing an expansive constant ε, the authors write Kψ=supn Kψ(ε, n) and define ν(E)={ψ : Kψ < ∞}. For f : E → E, as some applications of a theorem by Ruelle[3,Theorem 2.1], the authors show that each ψ ∈ν(E) has a unique equilibrium state. The conclusions eneralize the main result of Zhou and Luo[12].