The utility model discloses a device for a manufacturing large size optical fiber preformed rod, comprising a mandrill clamp, a quartz sleeve, an extension furnace and an extended rear handle clamp arranged successively. The mandrill rear handle is clamped in the mandrill clamp. A preformed rod extended rear handle is clamp in the extended rear handle clamp and the mandrill is clamped between the mandrill rear handle and the preformed rod extended rear handle. The mandrill is sleeved in the quartz sleeve. One end of the quartz sleeve is disposed in the extension furnace and the quartz sleeve is connected with a sleeve rear handle which is connected with a sealing device. An exhaust hood is arranged outside the sealing device and a sleeve clamp is clamped on the sleeve rear handle. The device is able to reduce the requirements of geometric accuracy and evenness of large size mandrill so that the large size mandrill manufactured by vacuum arc deposition process is suitable for a method for manufacturing a large size quartz optical fiber preformed rod.