Banded structure is a defect in steel, which can be divided into primary banded structure and secondary banded structure. The existence of banded structure makes the structure of steel uneven, and seriously affects the property of square tube, reduces its plasticity, impact toughness, fracture toughness and section shrinkage rate, and forms cold-bending and high scrap rate. When the heat treatment is stopped, the square tube is easy to deform and crack during quenching. To improve this problem, we can take the following four methods: one rolling process, the first banded structure appears in the continuous casting process, but the reasonable rolling process can effectively restrain the second banded structure. The parameters such as heating system, starting temperature, deformation, finishing temperature and cooling rate are especially important in rolling process. The billet heating can homogenize the segregation of as-cast microstructure and reduce the deformation resistance of square tube during rolling. In the allowed conditions, as far as possible to use a higher heating temperature, but also to ensure that sufficient heating time. Two steel grade composition, steel grade composition design, to properly handle the increase in the transformation temperature of the elements and reduce the transformation temperature of the relationship between the elements. If the influence of several elements can be counteracted and the difference of transition temperature between Dendrite and in Dendrite can be reduced, the banded structure of square tube can be reduced. In the process of triple heat treatment, the pre-eutectoid ferrite precipitates abundantly and the banded structure is aggravated due to the cooling in the furnace. During normalizing, the cooling rate is faster and the banded structure can be reduced. In isothermal normalizing process, the steel is heated and kept warm for a period of time, rapidly cooled to a certain temperature in pearlite transformation zone, then stopped heat preservation to complete the average transformation of ferrite and Pearlite, and then stopped cooling in air. In the four continuous casting process, the banded structure of steel after rolling is mainly due to the dendrite segregation in the continuous casting slab. Controlling the dendrite segregation and promoting the average distribution of elements in the continuous casting slab are effective methods to reduce or eliminate the banded structure. From the view of continuous casting technology, extending the equiaxed zone and obtaining fine secondary dendrite can effectively control the dendrite segregation. The equiaxed crystal region can be increased effectively by controlling the pouring temperature reasonably and keeping the constant speed. In addition, the reasonable secondary cooling process can control the surface temperature of the square tube, make the cooling average, and obtain the equiaxed crystal in large area.