The invention relates to nostoc flagelliforme polysaccharide oral liquid and a preparation method thereof. Based on a formula, the oral liquid comprises 0.01 to 0.05 percent of nostoc flagelliforme polysaccharide, 1 to 10 percent of fine acacia honey, 0.01 percent of vanillin, 0.1 to 0.2 percent of nisin, 0.2 to 0.3 percent of citric acid serving as acidulant and the balance of pure water. The nostoc flagelliforme polysaccharide oral liquid obtained by processes including raw material treatment, filtration sterilization and the like contains rich nostoc flagelliforme polysaccharide and acacia honey and has the functions of reducing blood sugar and blood fat, effectively removing radicals in human body, resisting aging, increasing body immunity and the like. In addition, the formula of the liquid is excellent, so the liquid is agreeable for old and young people to drink for a long time.