In this study, a multifunctional high‐vacuum system was established to measure the elec-tro‐optical conversion efficiency of metamaterial‐based thermal emitters with built‐in heaters. The system is composed of an environmental control module, an electro‐optical conversion measurement module, and a system control module. The system can provide air, argon, high vacuum, and other conventional testing environments, combined with humidity control. The test chamber and sample holder are carefully designed to minimize heat transfer through thermal conduction and convection. The optical power measurements are realized using the combination of a water‐cooled KBr flange, an integrating sphere, and thermopile detectors. This structure is very stable and can detect light emission at the μW level. The system can synchronously detect the heating voltage, heating current, optical power, sample temperatures (both top and bottom), ambient pressure, hu-midity, and other environmental parameters. The comprehensive parameter detection capability enables the system to monitor subtle sample changes and perform failure mechanism analysis with the aid of offline material analysis using scanning electron microscopy, energy dispersive X‐ray spectroscopy, and X‐ray diffraction. Furthermore, the system can be used for fatigue and high‐low temperature impact tests.