Abstract: Computational criteria used to judge the correctness of numerical calculation for sound propagation in ducts,are presented in the paper.An improved finite-difference scheme is proposed to compute problems with the discontinuity of the wall impedance.Moreover,the comparison of curves of numerical solution with experimental results for sound propagation in hard-soft-hard wall ducts and other examples are also presented.It is shown that both the criteria and the approach to discontinuity are successful and the computational model is rational.