This chapter comprehensively elucidates the pivotal role of gut microbiota in human health and disease prediction, highlighting that compositional and functional shifts serve as early biomarkers for obesity, metabolic syndrome, and neurodegenerative disorders. Critical tea bioactive compounds—including polyphenols, polysaccharides, and theanine—orchestrate gut microecology remodeling through multi-tiered mechanisms: structurally, they selectively enrich probiotics and SCFA-producing bacteria while suppressing conditional pathogens; metabolically, they enhance short-chain fatty acid production to fortify intestinal barrier integrity, precisely modulate bile acid metabolism, and rebalance tryptophan metabolism; systemically, they improve bile acid homeostasis and hepatic lipid metabolism via the gut-liver axis, while influencing neurotransmitter synthesis through the gut-brain axis to mitigate brain dysfunction. These findings underscore tea's potential in preventive health and disease intervention, offering modern scientific evidence for the health benefits of traditional tea consumption.