The boiler steel structure includes such parts as beams, columns, supports etc, and is the force bearing part and support structure of the boiler. Generally, the boiler steel structure can be categorized to structural type and girder type according to boiler models, bearing mode and loading nature. The medium and small boiler is always bearing typed, with light oven wall and tube-type air pre-heater. While, the large-volume boiler is normally installed outside the door, with pipe laying oven wall and slewing air pre-heater, and the weight of its heating surface is overhang through the suspender. So, the large-volume boiler is always girder typed to ensure the reliable working of its thermal expansion system.