In this study, the interactions between a Ga-based liquid metal (GLM)-GaInSn and some metal materials, including pure metals (Ni and Ti) as well as alloys (316H stainless steel (SS) and GH3535), at 650 °C were investigated. The goal was to evaluate their corrosion performance and select a suitable candidate material for use as the molten salt manometer diaphragm in thermal energy storage system. The results indicate that the alloys exhibited less corrosion in the liquid GaInSn, relative to the pure metals. For all the tested materials exposed to the liquid GaInSn, Ga-rich binary intermetallic compounds (IMCs) were found to be formed on the surface of the metal materials as a result of the decomposition of the liquid GaInSn and the reaction with the constituent elements of the metal materials. The corrosion mechanism for all tested materials exposed to the liquid GaInSn is also discussed and proposed, which may aid in selecting the optimal candidate material when liquid GaInSn is used as the pressure sensing medium.