The invention discloses a preparation method and applications of calcium/zinc composite thermal stabilizing additive used for polyvinyl chloride. The preparation method comprises the following steps of: uniformly mixing calcium stearate and zinc stearate according to the weight ratio being 5:1, arranging a mixture of the calcium stearate and the zinc stearate into an oil bath, heating, melting, forcefully stirring and taking out the mixture, cooling and grinding to obtain the calcium/zinc stabilizing additive; monitoring the thermal stabilizing effect of PVC (Polyvinyl Chloride) caused by calcium/zinc stabilizing additive, pentaerythritol and hydrotalcite by a monitor, and obtaining a composite proportion of the calcium/zinc stabilizing additive, the pentaerythritol and the hydrotalcite by taking detection data as basis, using torque rheometer and combining orthogonal experiment, mechanically stirring, mixing and cooling the calcium/zinc stabilizing additive and the pentaerythritol, then adding the hydrotalcite, mechanically stirring and mixing to obtain the finished calcium/zinc composite thermal stabilizing additive. The composite thermal stabilizing additive is used for polyvinyl chloride, the polyvinyl chloride and the composite thermal stabilizing additive are mechanically stirred and mixed according to weight parts, and the dynamic thermal stabilizing time is measured to be 69min through the torque rheometer. The method is simple, the composite proportion is accurate, and the optimal thermal stabilizing effect of the polyvinyl chloride is realized.