The invention discloses a preparation method of a pumpkin dietary fiber and the prepared pumpkin dietary fiber. According to the invention, pumpkin pulp is used as a raw material, which is treated with appropriate technology to remove starch and protein, so as to obtain insoluble dietary fiber and water-soluble dietary fiber; and purity of insoluble dietary fiber reaches higher than 85%, and purity of water-soluble dietary fiber reaches 90.5%. The dietary fiber provided by the invention has excellent quality, good water-holding capacity, swelling capacity and oil holding capacity; in addition, the dietary fiber has on sodium nitrite adsorption capacity, cholesterol adsorption capacity and cationic exchange capacity better than soybean dietary fiber on the market, has effects of lowering lipid, reducing weight and preventing cancer of pumpkin effects, and can be used as a functional food ingredient.