The 2.6～2.8 μm tunable laser setup based on single-resonant optical parametric oscillator(SRO)is designed and operated in order to get 2.7 μm tunable laser. The angle tuning curve and the effective nonlinear coefficient of Ⅱ(B)KTP optical parametric oscillator(OPO)are given. The cut angles of the crystal θ and φ are 62°and 0°respectively and the effective nonlinear coefficient is－2.97 pm/V. The 578 μJ output energy is obtained with the KTP SRO pumped at 1.064 μm TEM₀₀ mode laser,and the energy conversion efficiency is 1.7%. The output wavelength can be tuned from 2.6 to 2.8 μm.