A tunable multi-wavelength multiplexing spectrum modulation and separation system for high-power fiber laser amplification comprises a narrow linewidth seed source, a wavelength division multiplexing module, a spectrum modulation module, a first pre-amplifier, a wavelength separation module, a second pre-amplifier, a main amplifier and an end cap. The spectrum modulation module injects an electrical signal and adopts a tunable filter and a variable attenuator, so that the tunable spectrum line width can be realized, and the system has important application value in many different fields. According to the multi-wavelength common spectrum modulation broadening and separation system, multi-wavelength beam combination and high-precision and high-signal-to-noise-ratio separation can be achieved within the wave band range of 1.0 micrometer or 2.0 micrometers, meanwhile, the same inhibition effect on stimulated Brillouin scattering in multi-wavelength laser high-power optical fiber amplification is achieved, the consistency is shown in laser output power improvement, and the system has the advantages of being high in integration degree, simple in structure, convenient to control and particularly low in manufacturing cost, and miniaturization integration, array expansion and application of large-scale laser array synthesis are greatly facilitated.