The invention relates to an emulsion breaking agent with a defoaming function for extraction fluid treatment of ASP flooding and a preparation method of the emulsion breaking agent. The emulsion breaking agent mainly solves the problems that the running cost is high and the workload is high since the emulsion breaking agent and a defoaming agent are separately added. The emulsion breaking agent is characterized by being prepared from the following components by weight percent: 2.5 to 5 percent of polysiloxane, 2.5 to 5 percent of polyether modified polysiloxane, 30 to 40 percent of blocked polyether, 1 to 2 percent of emulsifier tween 80, 10 to 20 percent of water, and 40 to 50 percent of isoamyl alcohol. The invention also provides the preparation method of the emulsion breaking agent. The preparation method comprises the following steps: separately measuring all raw materials according to the weight ratio, dissolving the blocked polyether in the isoamyl alcohol, and preparing a solution A; then mixing the polysiloxane, the polyether modified polysiloxane and the emulsifier, and preparing a solution B; and adding the solutions A, B and water into a mixing kettle, and continuously stirring for 2 to 3 h. By adopting the emulsion breaking agent with the defoaming function, the requirement of the water purifying function and the defoaming function of the ASP flooding extraction fluid can be met, and the field dosing workload and the running cost can be reduced.