Recently the research about technical ceramics knows a renewed interest. The synthesis process of nanopowders plays a significant role in the production of such materials. This work, concerns particularly the synthesis of the nanopowders by laser pyrolysis. A numerical model is developed in order to understand the influence of the heat transfers occurring in the reactor and around the reaction zone, for a better control of the process. The study highlights the importance of the thermal transfer in the cell. A simple one dimensional analysis enabled us to define a stability condition of the flame function of the precursor flow rate and the cell pressure. The extended 3D calculations underline the complex fluid flow and heat transfer developing in the synthesis reactor.