The invention discloses an evaporating pipe. A fuel oil nozzle extends in from the inlet end of the evaporating pipe. The inlet end of the evaporating pipe is provided with a cyclone used for converting air flowing through the cyclone into rotary airflow. The cyclone is arranged between the evaporating pipe and the fuel oil nozzle and is located behind a spray opening of the fuel oil nozzle. An inlet of the evaporating pipe is provided with the cyclone, thus airflow in the evaporating pipe changes from non-prewhirl high-speed airflow into the rotary airflow. The rotary airflow can effectively reinforce the oil and gas premixing degree, the adverse impact caused by the difference of fuel oil flow of the spray opening of the fuel oil nozzle matched with the evaporating pipe in long-term work is avoided effectively, meanwhile, the rotary airflow can prolong the residence time of an oil and gas mixture in the evaporating pipe, then the time of oil and gas mixing is prolonged, the heat exchange area of the oil and gas mixture and the evaporating pipe wall is enlarged, the fuel oil atomization-evaporation rate is increased substantially through the high-temperature evaporating pipe, thus oil mist at an outlet of the evaporating pipe is distributed more evenly, and the performance of a combustor is ensured.