Abstract: Nano-CaCO3 particles were firstly modified using liquid polymer modifier, and then were used to prepare CaCO3/PVC composites by melt blending. The thermal degradation kinetics of pure PVC and its composites were discussed using Friedman method and Kissinger method. The results show that the degradation mechanism of pure PVC and its composites were consistent at the first stage of degradation, and their thermal degradation were both temperature and time dependent. The thermal degradation rate of PVC material was changed only by adding modified CaCO3 particles, but thermal degradation mechanism was not changed.