Based on pyrolysis technology, natural rubber can be converted to gases of high calorific value and then be used as fuels. In order to further explain the generation mechanisms of natural rubber pyrolysis gas, a combination of reaction molecular dynamics (RMD) simulations and thermogravimetry-infrared spectroscopy (TG-FTIR) experiments were used to study the pyrolysis process. The results show that the pyrolysis gases include CH4, C2H4 and a small amount of C3H6 and C4H6. The TG-FTIR also shows the presence of CH4 and functional groups (-C-H, -CH2, -CH3 and -C=C-) in C2H4, C3H6 and C4H8. The kinetics data of each reaction which obtained based on the chain reaction mechanism and transition state theory, were input into Aspen Plus process simulations to further get reasonable reaction path. The simulation results show that CH3 separated from the main chain abstracts H from other molecules to generate CH4, while C2H4 is mainly generated by the breaking of C-C bonds on long chains. Other small gas molecules are generated by the breaking up of large olefins or free radicals with low activity. This study provides a theoretical basis for the recycling of pyrolysis gas and may ultimately help to increase the energy efficiency of the pyrolysis process.