A pyrolysis process could utilize a large quantity of natural rubber to produce fuel for energy needs, but the poor pyrolysis performance of natural rubber limits this development. Co-pyrolysis can modify the pyrolysis of natural rubber to improve efficiency and the quality of pyrolysis products. Therefore, in this paper, thermogravimetry-gas chromatography (TG-GC) combined with molecular dynamics simulation was used to investigate the copyrolysis mechanism of natural rubber and cellulose. The results show that the copyrolysis process produced small molecule gases (i.e., H-2, CO, CH4, C2H6, C2H4, and C3H8) during the stages of intensity and residue pyrolysis. In addition, increasing the cellulose blending ratio can improve the pyrolysis conversion rate, small molecular gas (i.e., H-2, CO2, CH4, C2H6, C2H4, and C3H8) production, and reduce the temperature range of natural rubber pyrolysis, which enables an easier reaction in the pyrolysis process. Finally, with the increment of the cellulose ratio, the combination reaction leads to an increase of H-2 and CO production, while the yields of CH4 and C2H4 first increase and then decrease.