In this paper, on D we define Cowen-Douglas function introduced by Cowen-Douglas operator M * φ on Hardy space H 2 (D) and we give a sufficient condition for Cowen-Douglas function, where φ ∈ H ∞ (D). Moreover, we give some applications of Cowen-Douglas function on chaos, such as application on the inverse chaos problem for φ(T ), where φ is a Cowen-Douglas function and T is the backward shift operator on L 2 (N).