Abstract: In order to overcome the drawback that the sound absorption band of traditional cavity resonance anechoic coating is narrow,the functionally graded anechoic coating with periodic voids is designed in this paper according to the characteristics of Functionally Graded Materials(FGMs),and the Graded Finite Element Method(G-FEM) is employed to establish the underwater acoustic calculation model for functionally graded anechoic coating,and then the underwater sound performance of functionally graded anechoic coating is investigated.Compared with the traditional method for establishing the acoustic model of functionally graded structure,the proposed method can be extended to establish the acoustic model for much more complex functionally graded structures on the basis of ensuring calculation accuracy and efficiency.Numerical results indicate that,the functionally graded anechoic coating can improve the sound absorption performance in the middle and high frequency bands and wideband sound absorption can be achieved.In addition,the absorption frequency band of functionally graded anechoic coating can be effectively broadened by embedding the conical cavity or the combined cavity compared with the cylindrical cavity.