To identify the reactive sulfur species (RSS) made from alliin, the pure alliin solution was heated at 363.15 K and RSS were analyzed by HPLC-mass spectrometry (MS), tandem mass spectrometry (MS/MS) and ultra-pressure liquid chromatography-high resolution mass spectrometry (UPLC/HRMS). The results showed that RSSs made from alliin included allyl alanine disulfide, trisulfide, tetrasulfide, and dialanine disulfide, trisulfide, tetrasulfide. The allyl alanine tetrasulfide is a new compound which was discovered firstly. Besides, these RSSs were also firstly founded from the thermal decomposition of alliin. S-Allyl-L-cysteine can be generated directly from the thermolysis of alliin, which is a completely new-founded way. In conclusion, Rss could be founded from alliin when heated and may explain the functional effect of processed garlic such as black, salted, sugared once.