The effects of codopants and the deposition parameters such as gas flowrate and pressure in tube during the fabrication of fiber performs are studied. It is found that the fluorescence spectrum of Yb3+ can shift when codoping other elements, according to which, a double cladding Yb3+-doped fiber that is beneficial for 1018 nm laser is fabricated for the first time. When the fiber length is 7 m, an output of 22.8 W at 1018 nm is obtained. The optical-optical conversion efficiency is approximately 70%, and there are neither spontaneous radiation nor saturation.