A double-clad optical fiber fabrication method including the steps of: preparing a crystal fiber, inserting the crystal fiber into a silica capillary, attaching a sapphire tube to the periphery of the silica capillary, and applying a laser beam to the sapphire tube to increase the temperature of the sapphire tube and to further fuse the silica capillary with thermal radiation to have the fused silica capillary be wrapped about the crystal fiber, thereby forming the desired double-clad optical fiber.