This study deals with a method to simulate transient responses of tapered fluid lines with rigid pipe walls. The fundamental equation employed in this analysis is a transfer matrix based on a fluid line model in which the frequency-dependent effects of viscosity are considered. For the convenience of simulation, we employed a method for modeling irrational transfer matrix elements of the line by modal approximation. The resulting models were estimated as highly accurate by comparing them with the corresponding exact solutions in frequency domain. By applying these approximation models to a block diagram representation, simulated results of transient responses were calculated. The simulated results of pressure and flow rate responses were compared with the corresponding analytical solutions. As a consequence, the validity and applicability of the proposed method were well confirmed.