The invention relates to a method for preparing high-concentration fructose syrup by hydrolyzing sucrose, which comprises the following steps: (1) decolorizing a high-concentration sucrose solution by using acid with dosage accounting for 0.1-1.0% of the high-concentration sucrose solution as the hydrolyst while adding 0.05-0.8% of powder active carbon, and carrying out the reaction at 50-80 DEG C for 15-75 minutes to obtain the high-concentration fructose syrup of which the concentration is more than or equal to 45%, wherein the degree of hydrolysis is more than or equal to 97%; (2) and removing acid radicals and a small amount of pigments in the fructose syrup by using weak-base anion-exchange resin, and removing cations by using a strong-acid cation exchange resin, thereby adjusting the pH value of the fructose syrup. Compared with the exisiting method, the method of the invention is simple and convenient. Through deep research into the hydrolysis conditions, the invention provides the hydrolysis conditions capable of ensuring the hydrolysis effect and reducing the production cost. In addition, the invention carries out the hydrolysis and the decoloring synchronously, thereby ensuring the appearance of the syrup and simplifying the production technology. Then, the acid radicals and the cations in the syrup are removed by using anion and cation exchange resins, thereby obtaining the qualified high-concentration fructose syrup.