Hermetically Sealed Electromagnetic Relay (HSER) is widely used in high-reliability fields such as aerospace, where thermal stability is critical to ensuring operational performance and service life. To address the accuracy and efficiency issues of thermal analysis in such demanding applications, this paper proposes a modeling method specifically tailored for HSER. The method first derives a two-port unit topology model based thermal networks modeling method. The model is then implemented in Simulink to construct a thermal circuit diagram capable of simulating the temperature rise behavior of the relay in the released state. A detailed three-dimensional geometric model of the relay is developed in ANSYS, and steady-state thermal analysis is performed. Simulation results are rigorously compared with experimental measurement values. The maximum error of the finite element model is less than 2.5%, while the error of the thermal network model is controlled within 4.5%. The latter exhibits significantly higher computational efficiency, making it particularly suitable for rapid thermal assessment and optimization during the early stages of product development.