A high thermoelectric (TE) figure of merit zT of materials enables a high energy conversion efficiency. The quantity zT is defined by the Seebeck coefficient ( S), the electric ( σ) and thermal ( κ) conductivity, and the absolute temperature ( T). In this paper, we report on a computational model of the Combined ThermoElectric Measurement (CTEM) apparatus, which is a simultaneous characterization method capable of measuring the full set of above-mentioned thermoelectric transport properties between −190 and 600 °C. Currently, the measurement results show deviations due to unidentified error sources. As a solution approach of identifying possible error sources, a digital twin of the CTEM was developed. The computational thermal-electrical circuit model mainly consists of thermal sieving chains representing the relevant sample holder components, in particular two metallic blocks and a TE sample. For a computational consistency check of the measuring principles, ideal conditions are assumed, while no potential error sources are implemented, yet. Here, we present the measurement principles and procedures of creating the computational model of the CTEM. After studies on local discretization, the computational model undergoes a consistency check for model validation. The deviations between input parameters and simulated results of the three mentioned thermoelectric properties have been found negligibly small (≪1%) for ideal measurement conditions. This agreement certifies a realistic representation of the behavior of the sample holder by the digital twin with a satisfying reproduction of ideal measurement conditions by simplifying assumptions and the applicability of underlying measurement principles and evaluation protocols.