The characteristics of co-doping Al3+ in ytterbium-doped silica-based fiber used for high-power cladding pumped laser were analyzed based on experimental analysis. The results show that the optimum mole percent of Al3+ to Yb3+ is 9—11 for high concentration of ytterbium-doped silica-based fiber at which low concentration quenching probability, high absorption coefficient and proper numerical aperture can be obtained. Meanwhile, ytterbium-doped silica-based fiber preforms were fabricated by MCVD and special solution doping technique. By soot layer temperature experiment and test of the related parameters of the drawn fiber, the results show that the optimum temperature for making soot layer can be accurately controlled and the absorption coefficient at 976 nm was as high as 620 dB/m with good repeatability. This conclusion makes a useful reference for fabrication of ytterbium-doped Al3+ co-doped fiber.