The heat stabilizer N-butylmaleamic acid lanthanum (LaX3) was synthesized in two steps using n-butylamine, maleic anhydride, lanthanum chloride and sodium hydroxide as raw materials. The structure of LaX3 was represented by Fourier transform infrared spectroscopy (FTIR), and the thermal stability of PVC was determined through Congo red test. Then the effect of different heating rate on PVC pyrolysis reaction was studied using thermogravimetric analyzer, and the pyrolysis activation energy of PVC and PVC/LaX3, was obtained through dynamic calculations based on Flynn-Wall-Ozawa (FWO) method. The results showed that after adding LaX3, the heat stability temperature of PVC has increased by 32 ℃ and the heat stability time has increased by 15 min. Meanwhile, the reaction activation energy has increased by 33.53 kJ/mol. In conclusion, LaX3 can be used as a heat stabilizer for PVC.