This standard specifies testing methods for multiple key performance indicators of flexible graphite sheets, aiming to evaluate their chemical purity and thermal stability. It applies to the determination of ash content, fixed carbon content, thermal weight loss, sulfur, chlorine, and fluorine content, with the measurement range for sulfur content, for example, covering from 50 μg/g to 10000 μg/g. Additionally, the new version of the standard includes testing requirements for radiation resistance. According to the standard, completing these tests requires a series of specialized chemical analysis and thermal analysis instruments, mainly including high-frequency infrared carbon-sulfur analyzers for elemental quantification, analytical balances for precise weighing, muffle furnaces for high-temperature ashing tests, and thermogravimetric analyzers for assessing thermal stability. These methods collectively provide a unified technical basis for controlling the material quality of flexible graphite sheets and determining their suitability for applications such as sealing products.