This work describes a modeling study of methane pyrolysis in chemical vapor deposition (CVD). The model consists of a detailed chemical kinetic model, which includes 241 species and 909 gas-phase reactions for methane pyrolysis mechanism, and a plug-flow model, which describes the transport conditions in CVD. Reasonably good agreements were obtained between the simulation results and the experimental results of methane pyrolysis in CVD of pyrocarbon in a vertical hot-wall deposition reactor without any artificial adjustments. The mole fractions of hydrogen, acetylene, ethylene, and benzene increased with a decreasing growth rate as the residence time and the initial methane pressure increased. Sensitivity analysis and reaction paths were conducted to identify the crucial reaction steps and explain how they impact in this pyrolysis process. Results showed that methane pyrolysis had an incubation stage to form a necessary gas atmosphere for the pyrolysis to move forward and C-3 species were the main direct source for benzene formation. These results should be useful to understand methane pyrolysis at a molecular level in CVD, as well as the relationship between the gas species and the pyrocarbon.