Experimental results of a highefficiency 2.7 μm tunable laser are demonstrated on a quasiphasematched singly resonant optical parametric oscillator (OPO) in PPMgO\:CLN (5% MgOdoping) crystal pumped by a 1064 nm laser. Theoretical analysis of the PPMgO\:CLN temperature tuning is presented. When the crystal is operated at 150 ℃ and the pump power is 182 W with a repetition rate of 10 kHz, an average output power of 36.7 W at 2.73 μm is obtained with a slope efficiency of 23.7%. The wavelength tunability of 3.0~2.6 μm can be achieved by adjusting the temperature of a 31.3 μm period PPMgO\:CLN crystal from 30 ℃ to 200 ℃. Compared with the results of theoretical analysis, the discrepancy of about 10 ℃ is found in experiment.