Given the extensive utilization of composite insulators in electricity systems, the unresolved decay-like fragmentation of the composite insulator is of paramount importance in the preservation of the system’s functionality in daily life. The core rod’s gas production during the thermal aging process has been verified, which may result in the silicone rubber sheath deforming and potentially rupturing. This study has created an innovative vacuum thermal aging experiment platform that enables the conduct of thermal aging tests under vacuum conditions, thereby further elucidating the process of gas generation and its consequential impact. In addition, this platform is capable of accurately monitoring and recording the gas pressure value in the heating chamber in real time, as well as gathering the gases generated by the thermal degradation of composite insulator core rods. The experimental results elucidate the characteristics of gas production, with a particular emphasis on the thermal press.