Abstract: The two dimensional(2D) IsoGeometric Finite Element Method(IG-FEM) is applied to predict the acoustic attenuation performance of silencing ducts.Acoustic eigenvalues of duct cross-section are obtained by 2D IG-FEM and then the Transmission Loss(TL) is calculated.Perforated boundary and sound-absorbing material boundary are also considered.TL results of a rectangular silencing duct agree well with those obtained from the FEM and the accuracy of the IG-FEM is verified.Test case of a round cross section demonstrates that IG-FEM obtains more accurate results than the FEM does at almost the same computation cost.Under several different structure parameter conditions,TL of test examples by the IG-FEM are well compared with 3D numerical method.The IG-FEM can accurately predict the TL over a wide frequency range.