Due to the great application potential in various fields such as spectral beam combination, photoacoustic spectroscopy and nonlinear frequency conversion, high-power spectrum-tunable fiber lasers have gained much attention in recent years. Based on a spectrum-flexible superfluorescent fiber source and the well-known master-oscillator power amplifier structure, we have demonstrated a 3 kW linewidth- and wavelength-tunable high-power fiber laser. The output central wavelength of the fiber laser can be tuned over 1065-1085 nm, and the 3 dB linewidth is adjustable over 2.4-13.8 nm.