Abstract: The vacuum pyrolysis furnace is an experimental device to study the reaction of radicals. The high temperature inside the furnace causes the decomposition of molecules into different small molecule radicals and other intermediates, which then continue to react to generate complex reaction products. The constant temperature zone of the conventional pyrolysis furnace is only about one-third of the entire heating zone length, and the temperature at the end of the furnace tube drops too quickly, resulting in the continued reaction of small molecule radicals and other intermediates under the change of temperature, which is not conducive to reaction kinetic measurements. In this paper, finite element simulation of the internal heating of the pyrolysis furnace is carried out by COMSOL simulation software, and the simulation results are experimentally verified by the pyrolysis device. By changing the resistance wire winding density of the main heating zone and increasing the additional back heating zone at the end of the furnace tube exit, a large proportion of the thermostatic zone in the pyrolysis furnace is achieved, and the proportion of the thermostatic zone can even reach 80% of the heating zone length, as well as the effect of rapid heating at the entrance and slow and controlled cooling at the exit, which greatly improves the internal heating of the pyrolysis furnace and facilitates the sampling and measurement at the end of the furnace tube and the study of the kinetics of the radical reaction. The optimized new pyrolysis furnace can also be applied in other fields, such as heat treatment, processing, preparation, sintering, welding and coating of some materials, for which the optimization of temperature distribution is also important.