When ignition under the bed is adopted for the circulating fluidized bed boiler, the ignition air duct and ignition fan shall be provided. When the ignition for the boiler is started, in order to ensure the combustion air consumption for the oil burner, its pressure head shall be higher than that in the ignition air duct of primary air, in this way it can be ensured that the oil burner flame and the heat generated move forward, thus obtaining good recycling effect. The function of ignition fan is to supply air from the rear of the ignition to the ignition air duct. Its air intake is hot or cold primary air, which only playing a part of pressurization. Due to its less application time, and it is only used for pressurizing the primary air, therefore its power and capacity are smaller.