For the exploitation of viscous oil with thermal methods, further enhancement of recovery efficiency would be achieved by raising the flow parameters of the fluid injected into the wellbore. A calculation model was established in order to evaluate the flow and heat transfer of supercritical multi-component heat fluid injected into a wellbore. The bottom parameters (temperature and pressure) and the thermal loss along the wellbore versus the inlet parameters (flow rate, temperature and pressure) were calculated; and the results were also compared with those under the circumstance of the injection of supercritical steam (water). The results show a monotonic relation between the flow parameters at the wellbore bottom and the injection rate; and the pressure at the wellbore bottom also changes monotonously with the inlet temperature and pressure. The rest pairs of inlet and bottom parameters exhibit more complex relationship. To ensure the supercritical condition at the wellbore bottom, the injection rate and the inlet temperature of supercritical multi-component heat fluid must be higher than those of supercritical steam at the same inlet pressure. Economic performance can be improved through reducing the thermal loss by selecting lower but appropriate inlet pressure. The selection of fluid parameters for the thermal exploitation of viscous oil would benefit from this work; and then, the requirements could also be determined for the study and design of energy and power supply for the exploitation of offshore viscous oil.