Abstract: A high power 30/600 μm ytterbium doped double-cladding fiber with excellent power stability was fabricated by MCVD in-situ vapor phase/solution doping technology. The dopants of the silica fiber core include Yb₂O₃, Al₂O₃ and P₂O₅. The master oscillator power amplifier configuration based on back pump was constructed to test the Yb-doped fiber performance. In the experiment, the power of the seed was 189 W, the total power of the pump power was 4767 W, and the maximum output power was 4120 W with a slope efficiency of 85%. In addition, no stimulated Raman scattering was found in the output laser spectrum, and the 3dB band width was measured to be 1.6 nm. The fiber laser continued to work for one hour, the output power was stable at 4.1 kW.