A starch-based food thickener with low molecular weight and a preparation method thereof, comprising the steps of: adding starch powders with 5%-30% moisture content into an atmospheric pressure low-temperature dielectric barrier discharge plasma reactor, regulating the discharge gap to 0.2 mm-0.8 mm at atmospheric pressure, the discharge input voltage to 30 V-70 V, and the discharge current to 0.2 A-2.4 A, subjecting the materials in a fluidized state to plasma action in the circulating system by regulating the air flow rate with controlling time longer than 0.5 min, and then taking out the product after the completion of the reaction, i.e., to obtain a starch-based food thickener with low molecular weight. The method has such advantages as a simple technique involved, low cost, recyclable processing, large processing capacity, superior reaction uniformity, etc., and is also capable of efficiently and quickly degrading the molecular weight of starch, e.g., by 1-3 order(s) of magnitude within a short time. Moreover, the product has a superior transparency, retrogradation stability, and a certain thickening effect.
