The digestive properties of garlic polysaccharides were evaluated by simulating digestion in vitro and their effects on the immune function and intestinal flora of healthy mice were investigated. The results showed that garlic polysaccharides exhibited good anti-digestive properties, and approximately 93% of garlic polysaccharides could not hydrolyzed after oral and gastrointestinal digestion and were utilized by microorganisms. The results of animal experiments showed that garlic polysaccharides could promote the growth and development of mouse spleen, and significantly promote the levels of IgA (34.56%)， IgM (39.56%) and IgG (106.22%) in serum as well as SIgA (61.54%) in feces. It also improved the intestinal environment of mice， including promoting the proliferation of beneficial bacteria(such as Bifidobacterium and Lactobacillus)， inhibiting the growth of harmful bacteria， and increasing the levels of acetic acid and propionic acid. This result demonstrated that garlic polysaccharides could act as prebiotics and enhance the immune function of the body.