This study focuses on the analysis of coupled heat transfer in a differential calorimeter, based on in-pile test data. The theoretical calculation method is developed by considering heat conduction, convection, and radiation. Additionally, a three-dimensional numerical simulation is conducted to compare and analyze the results. It has been observed that as the reactor power increases, the gamma heating of stainless steel and aluminum materials also increases in an approximately linear manner. When comparing the calculation methods, it can be deduced that there exists a significant thermal resistance at the cold end of the measuring cell. Based on the aforementioned analysis, the temperature calculated after modifying the numerical calculation model demonstrates a high level of agreement with the experimental data, with a maximum deviation of less than 2.46 °C. As the reactor power increases, the proportions of radiation and convection heat in both the calibration cell and the measuring cell also increase. Specifically, the proportion of heat dissipation in the measurement section of the calibration cell ranges from 0.72% to 1.51%, while in the measurement section of the measuring cell, it ranges from 3.69% to 9.41%. These values are relatively low, which is advantageous in minimizing the calculation deviation of gamma heating in materials.