The invention belongs to the technical field of the processing of chlorine-containing polymer products, which discloses a stabilizing agent used for producing PVC plastic products and a preparation method thereof. The preparation method is mainly and technically characterized by comprising the following steps: putting organic acid into a reaction kettle sequentially, heating to dissolve the organic acid, putting a catalyst and dissolving the catalyst; then, putting each metal compound sequentially, preparing an intermediate after dewatering, heating, discharging and cooling, then putting the intermediate, other lamellar compounds, an antioxidant, a light stabilizing agent, pentaerythritol ester, diketone, amino crotonate and a lubricant into a compounding kettle and producing the stabilizing agent used for producing the PVC plastic products after compounding and stirring. The stabilizing agent has the characteristics of no toxicity, high stability, superior consistency performance with resin and good weatherability.