The invention discloses a corn starch adhesive and a preparation method thereof. The corn starch adhesive is prepared from corn starch, potassium permanganate, sodium hydroxide, borax, sodium thiosulfate, sodium bentonite and water. The preparation method comprises the following steps of: grinding and screening the sodium thiosulfate; preparing pasty corn starch in a constant-temperature water bath; mixing the water, the potassium permanganate and the screened sodium bentonite in the constant-temperature water bath, and pouring into the pasty corn starch to prepare mixed solution; adding water to dissolve the sodium hydroxide, the borax and the sodium thiosulfate, and pouring into the mixed solution to prepare the finished product. The preparation process is simple, and the conventional equipment is not needed to be changed; during production, the temperature is low, and the energy consumption is low; and the produced starch adhesive has the advantages of good liquidity, strong adhesiveness, quick drying, high stability, no pollution, and can greatly improve the ring crush compression resistance and the tension strength of corrugated paper.