A high-power mid-infrared laser is presented. The temperature-dependent tuning curve of the output wavelength of OPO is obtained through theoretical calculation,and the wavelength change with the effect of the crystal′s heat expansion is analyzed. The MgO doped periodically poled lithium niobate (MgO:PPLN) is pumped by an acoustic-optical Q-switched Nd:YAG laser. Using the optical parametric oscillator (OPO) configuration,an average power of 53.2 W for both 1.75 μm and 2.71 μm laser is obtained when the pump power is 104 W,at the repetition rate of 7 kHz,the conversion efficiency is 51%. The conversion curve doesn′t reach the saturated area,so the output power should increase with a higher pump power under the damage threshold of the crystal.