The invention relates to a preparation method for ultrahigh-content malt syrup, which includes the following steps: (1) grain starch as material is added with water and produced into slurry, the dry matter concentration of the slurry is regulated to be 20 to 30 percent, the pH value of the slurry is regulated to be 5.8 to 6.2, and thermostable amylase is added into the slurry; (2) a cooker is used for cooking the slurry under 108 DEG C to 110 DEG C for 5 to 6 minutes, so that starch paste is obtained, the starch paste is liquefied to be hydrolyzed, the liquefaction time is 30 to 150 minutes, and after the temperature is increased to kill enzyme, aqueous maltodextrin solution is obtained; (3) the pH value of the aqueous maltodextrin solution is regulated to 5.0 to 5.2, the aqueous maltodextrin solution is added with diastatic enzyme, the bienzyme method or the trienzyme method is adopted to saccharify the aqueous maltodextrin solution, the saccharification time is 50 to 60 hours, and after the temperature is increased to kill enzyme, the ultrahigh-content malt syrup is obtained. According to the preparation method, low-DE value maltodextrin without needing filtration can be stably obtained, more than 85 percent of maltose can be obtained, and the method has a good application prospect.