The invention provides an optical fiber preform loose body sintering device and an assembly method of the optical fiber preform loose body sintering device. The device comprises a furnace core pipe, wherein a furnace core pipe air inlet is formed in the lower part of the furnace core pipe; a quartz inner sleeve and a lifting rod are arranged at the bottom of the inner side of the furnace core pipe; the lifting rod is used for installing and taking out the quartz inner sleeve; a buffer pad is arranged between the bottom end of the quartz inner sleeve and the furnace core pipe; inner sleeve lifting holes are formed in the upper part of the quartz inner sleeve; the lower part of the quartz inner sleeve is provided with an inner sleeve air inlet corresponding to the furnace core pipe air inlet; the lower end of the lifting rod is provided with a lifting rod hook which is matched with the inner sleeve lifting holes. The device provided by the invention has the advantages that the quartz inner sleeve is arranged in the furnace core pipe, so that a falling optical fiber preform loose body can be effectively and timely collected and taken out, therefore the problem that the furnace core pipe is scrapped due to the falling of the optical fiber preform loose body is solved, the furnace core pipe replacement frequency is reduced, the production efficiency is improved, and the production cost is reduced; the buffer pad is arranged, so that the risk that the furnace core pipe is cracked due to the falling of a vitrified preform is reduced, and the service life of the furnace core pipe is prolonged.