Abstract: Optical parameter oscillator (OPO) based on periodically poled lithium niobate(PPLN) crystal and quasi phase matching (QPM) are suitable for generating continuous wave (CW) and tunable coherent radiation in mid-infrared wavelength range 3μm~5μm, which has important applications in atmosphere pollution monitoring, remote sensing, laser radar, spectroscopy analysis, and military infrared countermine. The recent development and advantages of CW mid-infrared optical parameter oscillator base on PPLN crystal was introduced. Specifically, the progress of techniques to increase the output power, lower the pump threshold, widen the tunable range and narrow the linewidth was addressed. Currently, the researches of optical parameter oscillator based on PPLN crystal are focus on the four areas mentioned above. Along with the development of the pump laser and nonlinear crystal, it will make further progresses toward the direction of higher power, lower threshold, wider tuning range, and the narrower line width as well.