The invention discloses an improving method for a center cylinder of a power plant boiler separator. According to the method, the whole circle of a cylinder body is evenly divided into six small parts, the size is made small, the cylinder body can be effectively transferred with an industrial lift, erection of a high tower crane is needless, the risk factor is small, potential safety hazards are avoided, and the cylinder body can be welded and fixed more easily; and the strength is high after welding, the service life is long, using cost is low, there is no need to remove handrails in the hosting process, operation is convenient and easy, and mounting efficiency is high.