The invention discloses coix seed diet tea and a preparation method thereof. The coix seed diet tea consists of the following raw materials in parts by weight: 50-80 parts of coix seeds, 5-8 parts ofhoney, 2-5 parts of dandelion, 5-7 parts of Chinese yams, 5-10 parts of hawthorns, 5-10 parts of mint, 4-5 parts of rhizoma atractylodis, 2-5 parts of wild chrysanthemum flos, 10-15 parts of tea leaves, 6-8 parts of folium mori, 4-6 parts of peach flowers, 2-5 parts of roses, 5-8 parts of momordica grosvenori, 5-10 parts of konjaku flour, 5-10 parts of poria cocos, 5-8 parts of radix rehmanniae preparata, 6-7 parts of dogwood and 2-5 parts of a condiment. Due to adoption of the food material, namely the coix seeds with a great deal of dietary fibers, and various healthcare green food materialsand medicinal materials with high-quality proteins, vitamins and minerals, a diet food which is rich in nutrition, good in slimming effect, free of side effect, free of weight regain and good in taste is made.