A continuous spectrum method is proposed and applied for modeling the time-domain viscoelastic function of asphalt concrete materials. This technique, employing a Wiechert model for the relaxation function and a Kelvin model for the compliance function, is found to substantially enhance accuracy and consistency compared to existing methods. Furthermore, this paper shows how to determine a time-domain Prony series representation, which can be used efficiently for numerical analysis, such as finite element analysis, from the complex modulus in the frequency domain, based on the continuous spectrum method.