Abstarct: Due to the great benefits of viscoelastic pipes, the use of these pipes in various systems is rapidly increasing. The Kelvin–Voigt method is used to model the viscoelastic behavior of the pipe. In this model, the spring, along with a number of different elements of the spring and dashpot in a parallel composition, are in series. The results of this modeling are presented in the form of an additional term in the hydraulic equations of flow in the elastic pipes. The purpose of this study was to investigate the importance of the number of Kelvin–Voigt model elements and pipe lengths that can have a significant effect on the results of the curve of the creep response function and the pressures and velocities resulting from the impact of the water hammer in viscoelastic tubes, as well as the effect of pipe length on the results of the calibration of the viscoelastic parameters are investigated by the inverse transient-flow dissipation method. In this research, the parameters of different elements of the Kelvin–Voigt model are calibrated using the fmincon optimization function whose objective function is calibrated using the sum of squares of residues between values with precise elements and values with unknown elements. These values are defined in the objective function using two creeping functions and pressure. The calibration of parameters using the creep function is first introduced in this thesis. The governing equations for the simulation of unsteady flow are the hydraulic equations of flow in viscoelastic pipes, which are used to solve explicit characteristics method. By calibrating the parameters using the creeping function, the creep function error decreases with increasing number of elements. The pressure error is also reduced by increasing the number of elements and increasing the length of the pipe. In the calibration of parameters using pressure, in larger lengths, the pressure head error decreases with increasing number of elements.