Main girder for boiler steel structure

The invention discloses a main girder for a boiler steel structure. The cross section of the main girder comprises an upper first I-shaped section and a lower second I-shaped section which are mutually overlapped and are connected by a high-strength bolt on an overlapped surface, and the first I-shaped section and the second I-shaped section are respectively made of different steel products. The upper section and the lower section are respectively combined by two different steel products with different strengths, the requirements on strength and stability are met, consumption of the steel products is reduced, installation and transportation requirements in the construction process can be met, and safety and economy are achieved.