The invention relates to the technical field of defoaming agent preparation technologies, in particular to a preparation technology of a defoaming agent for landfill leachate treatment. The preparation technology comprises the following steps that first, the following raw materials of polyoxy-propyl polyoxyethyl propyl trialcohol ether, alkylphenol polyoxyethylene, water glass, calcium stearate and an organic foam removing and foam inhibitng synergist are added into a stirred tank, stirring is conducted for 20-40 minutes, and thus the raw materials are evenly mixed; and second, mixed liquid isplaced in an attemperator of 30-50 DEG C, and stirring is conducted for 1-4 hours. According to the defoaming agent prepared from the raw materials, foam removing and foam inhibition performance is high, using amount is less, and the basic property of a foaming system is not influenced; heat resistance is good, chemical is stable, corrosion, toxicity, adverse side effects, burning and explosion are avoided, and the preparation technology of the defoaming agent is simple; and in the engineering of landfill leachate treatment, the defoaming agent is put into to serve as an auxiliary technologyof leachate treatment, the treatment cost is low, and the defoaming agent has the advantages of environmental protection, convenient using, good effect and the like.