The invention discloses a polyol ester metal complex PVC (Polyvinyl Chloride) thermal stabilizer and a preparation method thereof. The thermal stabilizer has a structural formula shown in the description, wherein M is magnesium, barium, zinc or calcium, and R1 and R3 each is C10-C18. The thermal stabilizer disclosed by the invention is esterified by adopting C10-18 straight chain fatty acid, thus,the thermal stability of the product is guaranteed, the compatibility with matrix PVC is improved, and meanwhile, the thermal stabilizer further has a lubricant effect. According to the thermal stabilizer, the preparation process is relatively simple, the influence on esterification caused by a charge effect of esterification after salinization is avoided through a method of metal salinization after esterification, and the prepared thermal stabilizer has excellent preliminary-stage and long-term thermal stability and weather resistance. Furthermore, shown by Congo-red experiments and torque rheological experiments, the product prepared by the method has relatively good thermal stability and lubricating property.