LAS120 online conversion health diagnosis system is composed of micro gas chromatograph, flue gas purification and pretreatment device, conversion health diagnosis software, which is a special health diagnosis system for sulfuric acid plant converter. It is suitable for the measurement of fractional conversion rate and leakage of heat exchangers for sulfuric acid production, smelting flue gas acid production, pyrite acid production, acid gas system acid and waste acid cracking acid production. The LAS120 has the advantages of fast measurement, accurate results and environmental friendliness.