The invention relates to a preparation method of flos lonicerae polysaccharide. Flos lonicerae is subjected to ethanol degreasing, air drying and extraction with boiling water, an extracting solutionis heated and concentrated for dialysis, an obtained dialysis internal fluid is heated and concentrated, 15v% trichloroacetic acid is added under the ice-bath condition, the mixture is stirred uniformly and neutralized and centrifuged with sodium hydroxide, precipitates are removed, a liquid supernatant is taken for dialysis, 80% ethanol is added to the obtained dialysis internal fluid, the mixture is left to stand overnight and then centrifuged, precipitates are collected, water-extraction flos lonicerae polysaccharide is obtained after drying and further purified with a DEAE (diethylaminoethyl) cellulose anion column and a Sephacryl S-200 HR column, and the flos lonicerae polysaccharide is obtained. The preparation method adopts a simple process and is convenient to operate, the preparedflos lonicerae polysaccharide can remarkably inhibit formation of HMEC-1 cell lumen, has a higher inhibition function on formation of the HMEC-1 cell lumen particularly when the polysaccharide concentration is 13.5 mu m and can be developed into an anti-angiogenic drug.