The antioxidative efficiency of thermal-reduced graphene (TrG) combining with antioxidant (AO, 3, 5-di-tert-butyl-4-hydroxycinnamic acid) on the thermal-oxidative stability of polypropylene (PP) was evaluated by examining the oxidation induction time (OIT) and the initial degradation temperature (Ti) of samples. The TrG was first prepared by thermal reduction of graphene oxide (GO) and was found to have a C:O ratio of 9.4:1. PP/AO/TrG compound incorporating with 0.5 wt.% of AO and 1.0 wt.% of TrG was then prepared by melt blending. The results revealed that a synergistically thermal-oxidative stabilization effect was formed between AO and TrG to cooperatively suppress the degradation of PP, resulting in the most outstanding thermal-oxidative stability compared with neat PP, PP/AO and PP/TrG compound. The synergistic stabilization mechanism of TrG and AO was discussed in terms of the concentration of peroxy radical and oxygen diffusion in PP matrix. It was proposed that the improved thermal-oxidation stability of PP/AO/TrG compound can be attributed to the decline in generation rate of peroxy radical due to the improved oxygen barrier property. The improved dispersion of TrG should be responsible for the better barrier property, which can increase the tortuosity of the diffusion pathways for oxygen molecules to form an effective labyrinth effect. The labyrinth effect of TrG on oxygen was efficient to retard the generation rate of peroxy radical, leading to the improvement of thermal-oxidative stability of PP.