Abstract: The stembase of Flammulina velutipes was pretreated by steam explosion, to explore the effects on antioxidant and anti-inflammatory activities of its water extract. The differences of active components in water extract of F.velutipes stembase before and after steam explosion were analyzed by ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS/MS). The contents of crude polysaccharides, total phenols and total flavonoids were determined by phenol-sulfuric acid method, Folin-Ciocalteu method and aluminum chloride method. The in vitro antioxidant capacity of water extract of F.velutipes stembase before and after steam explosion was determined by DPPH, ABTS and FRAP methods. The potential anti-inflammatory activity and mechanism of F.velutipes stembase water extract on LPS-activated cells were investigated. The results showed that the relative content of active compounds of F.velutipes stembase increased significantly after steam explosion, such as betaine, trans-3-indoleacrylic acid, adenosine and nicotinamide, which were 1.14 times, 1.32 times, 3.39 times and 3.21 times of that in the non-steam explosion group, respectively, and the content of crude polysaccharide increased by 56.03%. SFVE had better antioxidant activity, the DPPH free radical scavenging ability, ABTS⁺ free radical scavenging ability and Fe³⁺ reducing ability were 1.12 times, 1.07 times and 1.12 times of those in the non-steam explosion group (FVE), respectively. The anti-inflammatory result showed that the water extract of F.velutipes stembase after steam explosion had significant inhibitory activity on LPS-induced NO production in RAW264.7 cells (P<0.05), and the water extract of F.velutipes stembase could down-regulate the secretion levels of TNF-α, IL-1β and IL-6 (P<0.05). Therefore, steam explosion technology can be used as a new type of edible fungus waste pretreatment technology, which provides a new method for the development of functional food and is worthy of further study.