The invention relates to a fully-automatic vertical type circular seam welder which comprises a control console, a pressing mechanism, a welding gun, a rotary mechanism, a speed reducer and a motor, wherein the rotary mechanism is fixedly arranged on a rack of the control console in a vertical mode; the rotary mechanism is connected with the motor through the speed reducer; both the pressing mechanism and the welding gun are arranged above the rotary mechanism through the bracket; the pressing mechanism is equipped with a workpiece pressing column; the workpiece pressing column is in controlled connection with an air cylinder; the welding gun is equipped on the bracket through a welding gun clamp and is in controlled connection with the air cylinder; and an air cylinder on the pressing mechanism, an air cylinder connected with the welding gun and the motor are in controlled connection with a relay. The machine body of the circular seam welder adopts a vertical type structure, so that the circular seam welder is compact in structure and is small in floor space. In a welding process, a workpiece rotates on the horizontal plane, so that complex clamping positioning is not needed, and therefore, the operation is convenient and quick.