Abstract: Thermal degradation kinetics of SIS-PMMA in nitrogen has been studied using thermogravimitry. The relationship of degradation temperature and heating rate was deduced (Characteristic degradation temperature T=620.9 K), The activation energy of the SIS-PMMA in thermal degradation process is 270.9 kJ·mol~(-1),and thermal degradation mechanism is accord with Anti-Jander's equation:g(a)=1/(1-a)~(1/3)-1~2.