The convective heat transfer of carbon dioxide in the horizontal tube under supercritical pressure was simulated and the effects of heat flux density, wall temperature, mass flow and pressure on carbon dioxide convective heat transfer were analyzed. The results show that the influence of heat flux density and wall temperature on the heat transfer coefficient is relatively small, the influence of mass flow and pressure is more significant, the mass flow rate increases, the heat transfer coefficient increases significantly, the closer the pressure is to the critical pressure of carbon dioxide, the more obvious the change of heat transfer coefficient near the critical point, and the higher the peak value.