Abstract: Lanthanum itaconate was synthesized by saponification method, which was mixed with other components forming a compound thermal stabilizer for PVC. Thermal stability mechanism of PVC containing the compound stabilizer was studied by Congo red testing and FTIR. Processing performance and mechanical properties of the PVC compounds were determined by torque rheometer process tests and dynamic mechanics spectrometer. It showed that the best ratio was lanthanum itaconate∶pentaerythritol∶calcium stearate∶βdiketone was 3.5∶1∶1∶1. The static and dynamic thermal stability time reached 66.0 and 36.8 min, respectively, the early coloring of PVC was restrained. Processing performance and mechanical properties were similar to those of lead salt and lanthanum stearate compound systems and better than those of calcium zinc complex system. The FTIR showed that the compound thermal stabilizer could lower the reaction rate of HCl eliminating, and inhibit the formation of conjugated polyene at the beginning of the heating, and thus the thermal stability was improved.