Abstract: Based on the basic behaviors of the boundary layer, this paper analyzed the effects of buoyancy and flow acceleration resulted from the significant changes of thermal properties near the pseudo-critical region on the heat transfer of supercritical fluids near the wall. The theoretical thresholds of heat transfer deterioration, which resulted from buoyancy force and flow acceleration, were developed. Results showed that, for the heat transfer in the vertical flow, both buoyancy and flow acceleration would decrease the shear stress near the wall, and finally retrain the production and diffusion of turbulence. The thresholds of heat transfer deterioration resulted from buoyancy force and flow acceleration were Bu=1.16×10^-5 and Ac=2.91×10^-6, respectively. These thresholds agreed well with experimental data.