A practical method has been developed for numerically predicting pressure losses and acoustic characteristics in silencers simultaneously under the quasi-operating conditions of internal combustion engines. In the present method, three-dimensional gas flow and pressure dynamics in silencers have been numerically simulated by means of a new three-dimensional non-linear fluid-dynamic model, where the gas exchange process in entire intake and exhaust systems has been calculated by a one-dimensional non-linear fluid-dynamic model for saying the computing time. In this three-dimensional fluid-dynamic model, an accurate numerical scheme with less numerical diffusion has been applied to the Reynolds average Navier-Stokes equations using an eddy-viscosity hypothesis. Pressure losses and insertion losses in silencers have been examined using the three-dimensional model. It has been shown that the present method can predict the pressure losses and acoustic characteristics simultaneously.