The invention provides a health food for improving diabetes and a preparation method thereof. The health food is prepared from the following main extracts: undaria pinnatifida, eucheuma, bitter gourd,wolfberry, purslane, pumpkin seed, mulberry, fructus cannabis, rhoeo discolor, sea horse, mint, Chinese mosla herb, Japanese ardisia herb, schisandra chinensis, jasminum elongatum, honeysuckle, cynomorium songaricum, herba epimedii, gardenia jasminoides root, radix cynanchi paniculati, melastoma dodecandrum, fennel root, selaginella uncinata, pipewort, divaricate saposhnikovia root, common fibraurea stem, amomum cardamomum, piper cubeba, rheum officinale, fructus kochiae, golden hop, cortex lycii radicis, white lotus, rosin and calcined gypsum. The functional food provided by the invention isprepared by compounding effective extracts of sea-derived and land-derived medicinal and edible materials. Pharmacodynamic verification proves that the functional food can obviously reduce fasting blood glucose level of diabetes, prevents and assists in treating diabetes, and can be prepared into capsules, granules, tablets, pills or solutions.