A novel scheme for broadband mid-infrared (mid-IR) difference frequency generation (DFG) based on a temperature-gradient-controlled equal periodic PPLN is proposed. The theoretical results show that, under condition of the fixed pump wavelength, the acceptance bandwitdth (BW) of idler/signal quasi-phase matching (QPM) is increased with the temperature gradient across the crystal, whereas the conversion efficiency decreases. When the pump wavelength is 1.08 μm, the idler QPM BW is about 8 nm in the uniform temperature case. However, when the initial end temperature is 30 ℃, and the crystal temperature gradient increases to 20 ℃, 40 ℃ and 60 ℃, the idler QPM BWs are broadened to 35 nm, 80 nm and 136 nm, and the relative conversion efficiencies decrease to 0.2, 0.095 and 0.06. When the temperature at the initial crystal end and the temperature gradient are 90 ℃ and 60 ℃, respectively, the broadband idler QPM band moves to the shorter wavelengths and could cover the range of 3.288~3.464 μm.