The invention discloses a pretreatment method of ink for printing a packaging bag. The pretreatment method specifically comprises the following steps: S1: preparing raw materials; S2: preprocessing coal ash; S3: grinding the coal ash; S4: sieving the coal ash; S5: mixing the raw materials; S6: adding the mixed material obtained in the step S5 into ink to be treated, stirring the mixed material while adding the mixed material, reacting for 1h to 1.5h, standing for 30min, extracting a lower layer of precipitates, wherein a decolourization ratio reaches up to 90 percent or higher, and the removalrate of CODCr is greater than 70 percent. The coal ash is adopted as the raw material, so that the raw material is wide in source, and the production cost of the raw materials can be decreased; the block-shaped coal ash is pulverized and ground by virtue of a grinding machine, so that the coal ash is powdery, the subsequent mixing and stirring of the coal ash and the poly dimethyl diallyl ammonium chloride can be facilitated, the sufficiently-mixed material can purify the ink-containing waste water, the reaction time and the reaction temperature can be strictly controlled, the working efficiency is high, and the purification effect can be ensured.