In the design of domestic transmission high tower, the T-type welded structure of flange with bolt holes on the inner and outer circle and self-made large diameter steel pipe is first applied to two 370 m high towers of 220 kV Zhoushan and mainland power grid connecting project. However, the largest diameter for flange is up to 2.33 m, and for steel pipe up to 2 m. The traditional welding method for flange and steel pipe can not ensure the deformation precision of weld. Therefore, in view of the features of high tower, a new welding process of fine wire mixing gas shield is innovated and adopted, which includes setting reasonable groove angle, making welding sequence, providing measures to resist deformation etc. The results obtained in this paper will provide technical basis for welded structure design and application of large diameter steel pipe and flange in high towers.