A three-dimensional numerical simulation of the temperature field in high temperature combustion furnace is performed using a method of discrete ordinate to solve the radiation transfer and transfer coupled equations.A computer program of flow, combustion, heat transfer and NO_x turbulent formation is developed. The temperature distribution of Fuel Direct Injection (FDI) is numerically analyzed at different preheated air temperature and the validity of the applied numerical simulation is tested. The simulation results show that when preheated air temperature increases the maximum temperature gets larger, the temperature gradient becomes lower and the flame length longer.They are in agreement with experiments.