Rare earth complex and its preparation method and use

The invention discloses a rare earth complex. The rare earth complex is an N-alkyl maleamic acid-rare earth complex having a chemical formula of RE(OA)3.nH2O, wherein RE represents a rare-earth element; OA represents N-alkyl maleamic acid radical; and n is equal to 1 or 2. The invention also discloses a preparation method of the rare earth complex and a use of the rare earth complex in a polrvinyl chloride (PVC) heat stabilizer. The rare earth complex can be prepared by simple processes, and has a low cost and industrial application prospects. The rare earth complex or a composition of the rare earth complex as a PVC heat stabilizer overcomes the defects of the existing heat stabilizers, and improves primary dyeing properties and long-term thermal stability of PVC. Especially, the rare earth complex has good synergistic effects with calcium stearate, organic tin and pentaerythritol and thus under unified use, the thermal stability of PVC is improved. In addition, the rare earth complex can effectively improve mechanical properties of a PVC material.