Abstract: A numerical method considering anti-sound effects is proposed to calculate nonlinear sound propagation in varying area hard-wall ducts with transonic flow and without acoustic shock waves. By means of numerical examples, the effects of duct shapes, throat flow mach numbers, inlet sound source intensities and anti-sound intensities on nonlinear sound propagation are discussed in detail. It is also shown from the exmples that there does exist optimum anti-sound intensity at which the remarkable sound attennuation can be obtained at exit of the duct.