Abstract: Basic conditions of rotary piercing mills for hot-rolled seamless steel tube are briefly introduced, comparing Mannesmann(barrel type)piercer and cone type piercer for their piercing principles.Problems of the current rotary piercing process and the equipment structure are analyzed, an improving method is put forward and a new type of high rigidity rotary piercing mill is introduced.This new type of high rigidity rotary piercing mill adopts a design involving a billlet initiative rotating and centering mechanism on the front table, a lateral roll changing method and a fully-closed frame structure on the main body, and an on-line mandrel switching and quick changing device on the rear table.Therefore the piercing efficiency, the outer surface quality and the wall thickness precision of shells are increased and production cost is reduced.