By using a continuous wave (CW) Nd:YVO₄ laser as the pump source, the quasi-phase match is implemented for a PPMgLN crystal at room temperature and a continuous intracavity optical parametric oscillator (OPO) is obtained. The optical parametric threshold obtained is only 3 W (808 nm). For the pump power of 5 W and the period of PPMgLN crystal of 31.5 μm, both continuous mid-infrared laser output with the power of 365 mW at the wavelength of 2.95 μm and the signal laser output with the power of 312 mW at the wavelength of 1.66 μm are obtained. The total light conversion efficiency is up to 13.3%. By changing the periods of the crystal, the wide band tunable output of idle light in the spectral range from 2.95 μm to 4.16 μm and that of the signal light in the spectral range from 1.43 μm to 1.66 μm are obtained. This mid-infrared optical parametric oscillator is simple in structure and high in efficiency. It will be one of the important methods for producing 3-5 μm mid-infrared laser sources in the future.