Abstract: Gas phase combustion synthesis technology is a well-known chemical manufacturing technique for preparing nanomaterials. Nevertheless, the chemical reaction of precursors and the nucleation, growth, sintering and agglomeration of the nanoparticles make the whole combustion reaction zone be complicated. Flame chamber is the core equipment, and its structure affects the flow field parameters, ultimately determining the morphologies, structures and properties of the final products. In this work, three-dimensional geometric models of premixed high-speed jet flame reactors were developed, and the combustion simulations were carried out using k-ε turbulence model, Eddy Dissipation Concept (EDC) and discrete phase model. Additionally, a 19-step detailed reaction mechanism of H₂ was used for the temperature profile, velocity field and the particles residence time in high-temperature flame region. The effects of temperature, velocity and the reaction rate of H₂ combustion under different outlet diameters of the burner center duct were systematically investigated. The simulation results indicate that increasing the diameter of the outlet of burner center duct leads to significant increase in the length of the high temperature region, and the attenuation of the central jet velocity drops off in the different scales of flame reactors. SiO₂ nanoparticles were selected as discrete source in different scales of flame reactor, as well as for the study of residence time and back mixing in high temperature flame region. The results show that the residence time of the nanoparticles in the high temperature flame region is obviously increased, and the back-mixing phenomenon is aggravated. Together with the calculations, these results supply useful references for regulation and control of nucleation growth process of nanoparticles and provide theoretical fundamentals for industrial flame reactor design.