A cylinder welding system includes a welder that has a control unit, a welding head and a wire feed. Each of the wire feed and the welding head is electrically coupled to the control unit. A cart is provided and the cart is rollably positioned within a cylinder. A rotation unit is rotatably coupled to the cart and the rotation unit engages an inside surface of the cylinder. The rotation unit is electrically coupled to the control unit such that the control unit controls operational parameters of the rotation unit. In this way the rotation unit is actuated to rotate along the inside surface of the cylinder. The welding head is coupled to the rotation unit to weld the inside of the cylinder when the rotation unit rotates along the inside of the cylinder. In this way one cylinder may be automatically welded to another cylinder.