Poly α-methylstyrene (PAMS) is a typical α,α-disubstituted vinyl polymer material and has manifested excellent thermal degradation properties. It was widely used to prepare a variety of laser inertial confinement fusion targets. In this paper, the thermal degradation mechanisms of PAMS and the thermal degradation kinetics were reviewed. The effects of relative molecular weight, the end groups of PAMS, and initiators on the thermal degradation temperature of PAMS were introduced, and the principle of these factors was also summarized. Finally, the research direction of decreasing degradation thermal temperature of PAMS based on relative molecular distribution, constitutive regularity, optimizing initiators and heating procedure was proposed.