Abstract: Aim at the change problem of output beam direction when using a rotated out-coupling mirror as the tunable element, a laser system with constant direction of the tuned output beam was designed by shifting the gain fiber position. According to the grating equation, the tunable mechanism of shifting gain fiber was analyzed. Further, the changes of gain linewidth with the fiber position and mode field radius were also analyzed by means of the coupling model of the output and feedback beams, which show that the gain linewidth of the output beams for the designed fiber laser was less than 0.2 nm. The experimental results show that the maximum output power is 470 mW at 1543.446 nm, with a slope efficiency of 23.9%. The experiment also shows that the wavelength tunable range is 36 nm, and the 3 dB linewidths in the whole tunable range are less than 0.08 nm.