We use an acousto-optic Q-switched Nd∶YVO4 laser as the pump source and obtain a Nd∶YVO4 / PPMgLN optical parametric generator (OPG).The threshold value of OPO system is only 0.5 W (20 kHz,75 ns)at 1064 nm.When the pump power is 2.25 W (20 kHz,52 ns),a maximum idle laser output power of 426.1 mW at 3.03 μm,and a signal laser output power of 646.7 mW at 1.64 μm have been achieved,and this corresponds to a whole optic-optic conversion efficiency of 47.6%.By shifting the PPMgLN crystal,the periods of the domain structure on the PPMgLN wafer can be changed,thus enabling a widely tunable mid-infrared spectrum of 3.03~4.49 μm,and signal wavelengths widely tunable in range of 1.40~1.64 μm.