Experimental results of high-efficiency 2.7-μm laser is demonstrated on quasi-phase-matched single-resonated optical parametric oscillator (OPO) in PPMgLN (5% MgO-doping) pumped by 1064-nm laser. Theoretical analyses of PPMgLN grating period tuning are presented. When grating period is 31.3 μm, a PPMgLN OPO could get output at wavelength of 2.7 μm. The pump beam polarization matches the e→e＋e interaction in PPMgLN, thus maximal nonlinear coefficient d33 (27.4 pm/V) is effective and walk-off of beams can be avoided. When pump power is 26 W with repetition rate of 7 kHz, an average output power of 4.7 W at wavelength of 2.72 μm is obtained with slope efficiency of more than 21%, and 9 W at the corresponding idler wavelength of 1.75 μm. The M2 factors of 2.7-μm laser are 2.05 and 1.84 in parallel and perpendicular directions, respectively.