A method to control the distribution of the starch sugar's molecular weight by controlling of Ultra-low DE value during the reaction was invented. The method comprising blending starch with water to get starch slurry, and then mixing it with the 0.01%-0.03% of CaCl2 based on dried starch. The next step involves adjusting the pH of the starch slurry. A further step involves adding 0.03%-0.08% of heat-resisting α-amylases based on dried starch to the starch slurry described above. A further step involves controlling the production under optimal reaction conditions.