Pyrolysis process of important intermediate 1,3-butadiene from the pyrolysis of cyclohexane was studied theoretically. Standard enthalpy changes for the two possible pyrolysis reaction paths were computed by UB3LYP/3-21G * , UB3LYP/6-31G * , UB3LYP/6-31+G * and UB3LYP/6-311+G * . Thermodynamic and kinetic computation for the reaction paths at different temperature ranges was pursued by UB3LYP/6-31+G * because of its accuracy. The results show that (1) the pyrolysis temperature of 1,3-butadiene is above 1173K, main products are C 2 and C 4 species, and the possibility of getting C 2 species is more; (2) at a temperature range of 298-1473K, the reaction path 2 that starts with the broken C-H bond and produce C 4 species which is feasible from the viewpoint of thermodynamics; (3) the reaction path 1 that starts with the broken C-C bond and produce C 2 species which is feasible from the viewpoint of kinetics, and the reaction activation energy of the rate-determining step for path 1 is 452.60kJ/mol; (4) with increasing temperature, the rate constant of the rate-determining steps of the two reaction paths are nearer to each other, which means that both the reaction paths exist in the pyrolysis process. The above results are basically in accordance with the mass spectrum analysis of 1,3-butadiene, and is far more specific than experimental result.