of the exact solution, especially for the high wave numbers. In order to get reliable solutions for high wave numbers, a refined mesh or a higher order of the polynomial approximation can be applied. Through these schemes, the solutions can be improved, but this will result in large systems of equation; thus, the computation time will greatly increase. Thereby, the minimization or even the elimination of the pollution effect is strongly desirable. In the past years, a number of efforts have been spent on the development of FEM to achieve this aim. Thompson and Pinsky presented a Galerkin least squares FEM to reduce the dispersion [ 9 ], and Oberai and Pinsky developed the residual-based FEM to reach this goal [ 10 ]. Partition of unity finite element method (PUFEM) is another method, in which a priori knowledge about the solution of the problem is introduced into the FEM [ 11 ]. Unfortunately, this method will lead to ill-conditioned system matrices; hence, the use of the classical iterative solvers becomes complicated. In parallel with the FEM and BEM, meshless methods are relatively new numerical methods. As compared with FEM, no mesh is needed in meshless method for the discretization of the problems. On the contrary, the governing equations are discreted by arbitrarily distributed points. In [ 12 -- 14 ], meshless methods have been presented to solve practical engineering problems. However, using the meshless methods to solve the acoustic problems, especially the interior acoustic problem is relatively few. Element free