Abstract: The determination of carbon content in LiH was studied with HCS-878F high-frequency infrared C-S measurer. Various experiment conditions such as heating temperature, type and dosage of flux and sampling amount were studied. The results show that hydrogen in the example can be released during burning by increasing the power of the instrument step by step without fulmination. To avoid the influence of hydrogen released on the result of determination, a device for translating CO into CO₂ was installed in the gas road, so the carbon content in the sample can be determined quickly with better accuracy and precision. For sampling amount about 30 mg and carbon content of 500-3 000 μg/g, the relative standard uncertainty is less than 10%, and the recovery of carbon is 91%-108%.