Provided is a method for producing a large-diameter steel tube by using two blocks of arc panels with unequal wall thickness. A steel tube body is composed of two blocks of arc panels with unequal wall thickness, lofting and cutting are conducted on the basis of the arc central lines of the two blocks of steel panels, preparatory cutting is conducted on a straight panel thin steel plate and a straight panel thick steel plate, the straight panel sheet plate and the straight panel thick steel plate are full penetrated and welded into a block of whole straight panel, pre-pressing arc treatment is conducted, circular tube rolling is conducted from the end head position of the thin steel plate by using a three-roller plate coiler, arc formation on the position where the thin steel plate is in butt joint with the thick steel plate is gradually achieved, and arc rolling of the thick steel plate is continued till completed to enable the spliced whole straight panel to form a circular tube with to-be-welded openings; after the steel tube rolling is completed, rectification and correction and spot welding are conducted on a longitudinal joint between the end heads of the thick steel plate and the thin steel plate through a manual hoist correspondingly; and full penetration welding is conducted on the closed butt jointed longitudinal joint between the thick steel plate and the thin steel plate of the circular tube, and thus a large-diameter steel tube is formed. The method for producing the large-diameter steel tube is simple in method technology, low in butt jointed welding difficulty, and low in roundness correction difficulty.