This study conducted an in-depth analysis of the thermal characteristics of a comprehensive experimental setup for a thermionic reactor using SINDA/FLUINT software. SINDA/FLUINT is a comprehensive finite difference, lumped parameter, and finite element software used for thermal design analysis and fluid flow analysis of complex systems. It has wide applications in aerospace, electronics, energy, petrochemicals, and other fields. Its application prospects are broad, especially in the fields of energy and aerospace, and it is expected to become an important development direction in the future. During the research process, a heat transfer analysis model for TOPAZ-II space nuclear reactor was established, and numerical verification was conducted under different operating conditions. Through simulation analysis and steady-state and transient calculations of the reactor, the temperature distribution of the entire system and its components under two different conditions was obtained. The highest and lowest temperatures during operation were determined, and the key factors affecting the heat transfer characteristics of the device were revealed, providing important references for subsequent optimization design and engineering applications.