Two kinds of rare earth heat stabilizers, Dipentaerythritol lanthanum metal alkoxides (Di-PE-La) and Maleic acid dipentaerythritol maleate lanthanum metal alkoxides (DMPE-La), were synthesized from di-pentaerythritol, maleic acid and lanthanum acetate. On the one hand, the thermal stability of DMPE-La to PVC was investigated. The results showed that DMPE-La had better initial coloring performance and long-term thermal stability than Di-PE-La, and the tensile strength of DMPE-La was maintained, the elongation at break of the sample can be increased. On the other hand, the theoretical calculation and the study on the mechanism of heat stabilization show that both rare earth heat stabilizers can replace the unstable chlorine atom on the PVC chain to improve the initial coloring property of PVC and can absorb HCl, at the same time, the hydroxyl groups in two kinds of rare earth heat stabilizers can complexate ZnCl2, avoid ZnCl2 dissociation and catalyze PVC degradation.