A novel fiber-type widely tunable continuous-wave Mid-IR laser source was present and demonstrated. The Mid-IR laser system was based on the difference-frequency generation (DFG) and the quasi-phase-matched (QPM) techniques. The nonlinear crystal used is a periodically poled MgO-doped LiNbO3 (PPMgLN) crystal with multiple-periods structure. An ytterbium-doped fiber laser and a tunable laser cascaded with an erbium-doped fiber amplifier (EDFA) were used as the pump and the signal sources for the DFG process, respectively. With such a fiber-type QPM-DFG system, the continuous-wave Mid-IR radiation was obtained. It was found that the FWHM of the phase mismatching due to the temperature was about 4.5 ℃. By suitable choosing the crystal period combined with controlling the temperature and the wavelength of signal, Mid-IR radiation with continuously tuning range between 3.1 to 3.6 μm has been achieved with the system.