Lanthanum alpha-ketoglutarate was prepared by two-step method using alpha-ketoglutarate, lanthanum nitrate and sodium hydroxide as raw materials and water as solvent. The structure of the product was characterized by elemental analysis, ICP-OES and FTIR. The static thermal stability of the product to PVC was tested by Congo red test paper, the dynamic thermal stability of the product to PVC was tested by torque rheometer, and the effect of the product on the thermal degradation kinetics of PVC was studied by TGA. The synergistic properties of the product were investigated by compounding with auxiliary thermal stabilizers such as beta-dione, PDOP, PER and ESO, and the microscopic surface morphology of PVC degraded at different time was observed by SEM. The results showed that lanthanum alpha-ketoglutarate has good thermal stability for PVC. When 3 wt% was added, the static thermal stabilization time could reach 13 min and the dynamic thermal stabilization time could reach 1820 s. The average activation energy of PVC thermal degradation process could be increased by 15.78 KJ/mol. The synergistic effect between PER and the composite thermal stabilizer was the best. The static thermal stabilization time of composite thermal stabilizer for PVC was 37 min and the dynamic thermal stabilization time was 3480 s. SEM observation showed that the composite heat stabilizer could better inhibit the agglomeration of PVC.