Optical parametric oscillators based on periodically poled MgO-doped lithium niobate (PPMgLN OPOs) are ideal sources for high-power,continuously tunable mid-infrared (MIR) light,which is attractive for applications including laser spectroscopy,atmosphere detection and MIR countermeasure. In this paper,temperature tuning characteristic of PPMgLN OPO and oscillation threshold of pulsed SRO are analyzed theoretically. An OPO with PPMgLN pumped by Nd:YAG (1064 nm) Q-switched polarized laser is reported. The oscillation threshold is 1.7 W,which is close to the theoretical result. Idler output power of 1.35 W at 3.93 μm is achieved with pump power of 12.3 W. Idler wavelength output is tuned continuously from 3.846 to 3.952 μm with temperature varied from 60 to 140 ℃,which is in accordance with the theoretical tuning curve.