A broadband difference frequency generation (DFG) comb with high conversion efficiency based on a mode-locked erbium-doped fiber laser and GaSe crystal is presented. The DFG comb adopts all-polarization-maintaining fiber structure to obtain fundamental frequency pulses with high linear polarizations degrees, and the nonlinear pulse fiber amplification technique is utilized to achieve wide bandwidths, short durations and high peak powers, for the two-color fundamental pulses. This offers the DFG comb the properties of wide bandwidth and high conversion efficiency, and the stability of the DFG process. The experimental results show that the achievable bandwidth of the DFG comb near 8.15 μm reaches 1.7 μm, only limited by the phase-matching acceptance bandwidth of the crystal, and the corresponding DFG conversion efficiency is as high as 1%, much higher than that for the fiber-type DFG comb reported so far, which is about 0.4%.