Yttrium aluminosilicate (YAS) glass core fibers with different doping concentration of Tm3+ were fabricated by a Melt-in-Tube method from YAG polycrystalline ceramics. The effect of Tm3+ concentration on the spectroscopy of YAG ceramics and laser performance of YAS fibers were discussed. A homemade linear all-fiber laser based on the obtained 15% Tm3+-doped YAS fiber shows an optimized slope efficiency of 12.8%. The YAS fibers have been proven to be practical to achieve extremely high Tm3+ doping concentration and are a promising option for the 2.0m laser.