The invention discloses a butting process of a large-diameter rolled steel pipe for a building structure, comprising the following steps: (1), fattening pipe ends; (2), chamfering the pipe ends: chamfering to obtain dull edges 7-9 mm in size through a chamfering apparatus and a groove angle 22-25 degrees, and butting pipe segments to form a Y-shaped groove; (3), butting steel pipes; (4), pre-welding: applying mixed gas shielded welding and gas shielded welding wires, a gas being 80% of Ar and 20% of CO2, current being 140-160 A, voltage being 25-27 V and welding speed being 0.5-0.6 m/min; (5) welding inside and outside: carrying submerged arc welding for inside prior to outside, both using four-wire submerged arc auto-welding, and wires being 3.5-4.0 mm in diameter, welding speed being 1.0-1.2 m/min; (6), grinding for redundant height of a weld; (7), carrying circumferential weld UT detection; (8), carrying X-ray detection. The butting process of the rolled steel pipe enables greatly improved butting quality and efficiency of the steel pipe and reduced cost and can guarantee good appearance quality.