The invention discloses a cinnamomum japonicum phenolic compound and a preparation method and the application thereof. The cinnamomum japonicum phenolic compound is prepared by adopting Chinese medicine cinnamomum japonicum as a raw material. The preparation method comprises the following steps: (1) preparation of cinnamomum japonicum sample liquid: coarse cinnamomum japonicum powder is selected to be extracted by water, alcohol-water solution or aqueous acetone, the extracted liquid is merged to be filtered, the filtered liquid is decompressed, the ethanol or the acetone is recycled until the liquid is free from the alcohol smell or the acetone smell, appropriate water is added into the extracted liquid to be held and filtered so as to obtain the cinnamomum japonicum sample liquid; (2) preparation of cinnamomum japonicum phenolic compound: the cinnamomum japonicum sample liquid is precisely measured to be pre-absorbed by macroreticular resin column, the liquid is washed out by water,the water washed-out liquid is abandoned, then the liquid is washed out by thin alcohol of less than 30 percent, the thin alcohol washed-out liquid is collected, and the solvent is recycled to be made into dry extract. The compound can reduce the blood sugar with an insulin-sensitizing way, and can be used as a drug for treating diabetes or as a raw material of the healthcare food.