Abstract: The different proportions of Nano-diamond/ polypropylene(PP) composites were prepared by melt blending, and thermal degradation kinetics of the composite material was investigated by means of thermogravimetry analysis(TGA). The thermal degradation activation energy(Ea) of the blends was calculated by Flynn-Wall-Ozawa, Friedman and Kissinger methods. The results show that the non-isothermal degradation of Nano-diamond/PP composites is a one-stage degradation process and Nano-diamond could visibly enhance thermal stability of the composite material. However, the enhancement of thermal stability becomes obvious with the increasing of Nano-diamond concentration, and then slight. When the content of Nano-diamond is 3%, the enhancement stands at maximum. And the increase of thermal degradation Ea varies from 5 kJ/mol to 30 kJ/mol.