We report here a high-power, wavelength tunable and narrow linewidth $1.5~\unicode[STIX]｛x03BC｝\text｛m｝$ all-fiber laser amplifier based on a tunable diode laser and Er-Yb co-doped fibers. The laser wavelength can be precisely tuned from 1535 nm to 1580 nm, which covers many absorption lines of mid-infrared laser gases, such as $\text｛C｝_｛2｝\text｛H｝_｛2｝$, HCN, CO, and HI. The maximum laser power is $｛>｝$11 W, and the linewidth is about 200–300 MHz, which is close to the absorption linewidth of the above-mentioned gases. This work provides a suitable pump source for high-power wavelength tunable mid-infrared fiber gas lasers based on low-loss hollow-core fibers.