Abstract: Supercritical carbon dioxide (S-CO₂) is widely used in coal-fired thermal power generation, concentrated solar power generation and nuclear reactors because of its low corrosiveness, low critical parameters and high efficiency. In these conditions, S-CO₂ is usually turbulent flow with high temperature, high pressure and high heat flux. At present, the turbulence model is mainly used for subcritical and near-critical flow problems, whereas it is not suitable for supercritical fluid flow. Therefore, a study is carried out on the characteristics of S-CO₂ turbulent flow in a vertical tube under supercritical conditions far from the pseudo-critical point. A multi-fields coupled numerical model of S-CO₂ in a round tube with uniform heating is developed and validated by our experimental data. The effect of the turbulent Prandtl number (Pr_t) on the turbulence model is investigated, and the effect of key operating parameters is also discussed. The results show that Pr_t has an important effect on the heat transfer of the S-CO₂ turbulent flow with high heat flux. For the SST turbulence model, when Pr_t is reduced from 1 to 0.65~0.70, the mean relative error (MRE) of the inner wall temperature can be reduced by approximately 3.16% and the convective heat transfer coefficient can be increased by 25.21%. The modification of Pr_t can effectively improve the accuracy of SST turbulence modeld. This paper also provides a theoretical basis for the development of S-CO₂ cycle under high heat flux.