High-power　mid-infrared　(MIR)　lasers　have　aroused　great　interest　in　many　scientific　and　industrial　applications.　Due　to　the　immaturity　of　pump　sources　and　fiber　materials,　it　has　been　difficult　to　achieve　high-power　laser　output　in　MIR　long-wavelength　spectrum　(LWS)　exceeding　2.4　mu　m　using　traditional　schemes.　Here,　we　propose　a　new　method　for　generating　MIR　laser　that　utilizes　the　dispersion　characteristics　of　nonlinear　fiber　to　segmentally　regulate　the　frequency-shift,　accumulation,　and　enhancement　process　of　soliton　group　pulses,　in　order　to　maximize　pump　energy　conversion　and　reshape　spectral　profile.　A　14.72　W　high-power　all-fiber　MIR　laser　was　obtained　using　a　fluorotellurite　fiber　with　dispersion　specifically　engineered　as　a　frequency-shift　stretcher.　The　laser　conversion　efficiency　reached　70%,　facilitating　efficient　energy　conversion　from　2　mu　m　near-infrared　laser　to　3　mu　m　mid-infrared　laser.　Notably,　the　proportion　of　MIR　LWS　exceeding　2.4　mu　m　was　significantly　enhanced,　accounting　for　over　90%　of　the　total　spectrum　components.　This　work　provides　a　simple,　compact,　efficient,　stable　and　economical　method　for　developing　high-power,　high-efficiency,　and　high-occupancy　MIR　fiber　lasers,　without　the　need　for　complex　MIR　amplification　systems,　which　is　of　great　scientific　significance　for　promoting　the　practical　application　of　3-5　mu　m　MIR　light　sources.