Abstract: Ultrashort pulse source with high energy and tunable wavelength is highly demanded for a lot of applications. Amplified all-normal-dispersion(ANDi) mode-locked fiber laser with gain medium of Ybdoped fiber is a compact and excellent source that fulfills those requirements. In this paper, amplification of tunable ANDi Yb -doped mode-locked fiber lasers was experimentally investigated. The gain versus signal wavelength was analyzed. It was found that the maximum gain was obtained near 1 030 nm and the gain decreased as wavelength increased, due to the gain spectrum of Yb-doped fiber. The gain versus pump power was also investigated. Gain saturation and the effect of ASE noise on gain were observed. The spectral and temporal distortions of pulse seed induced by fiber amplification were discussed. The pulse was broadened slightlydue to dispersion. The spectrum was distorted by ASE noise and limited gain bandwidth. If the gain is large and the power of amplified signal is high, the spectrum will be broadened by the effect of self-phase modulation(SPM).