The invention discloses a method for preparing a doped optical fiber outer cladding layer, and the method comprises the following steps: 1) a deposition tube and a head tube are butted by fusion, and impurities are removed; 2) one end of a core rod is provided with a groove along the length direction of the core rod, the end, which is provided with the groove, of the core rod stretches into a negative pressure suction connection pipe, and the negative pressure suction connection pipe is heated for fusion fixing with the core rod; 3) one end, which is not provided with the groove, of the core rod stretches into the deposition tube toward the direction of the head tube, and the opening of the deposition tube is heated for sealed connection of the negative pressure suction connection pipe and the deposition tube; 4) the pressure of the deposition tube is pumped to a negative pressure, a blast burner moves from the head tube to the direction of the negative pressure suction connection pipe for heating to fuse the deposition tube and the core rod together. Through arrangement of the groove on one end of the core rod, when air is pumped, the groove plays a key role, air between the deposition tube and the core rod enters the negative pressure suction connection pipe through the groove, and a negative pressure system is formed in the deposition tube, so that the deposition tube and the core rod can be reliably fused.