The output of 2.7 μm wave band laser with high peak power is obtained by KTiOPO4 (KTP) crystal optical parametric oscillation (OPO) pumped by 1 064 nm laser. Experimental results are analyzed in detail. The pump source is an electro-optical Q switched Nd:YAG laser, and the OPO is singly resonated. Two identical KTP crystals are placed with opposite optical axis to compensate the walk off effect. The crystals are cut as ?=0°, θ=62° to generate 2.7 μm wave band laser. To utilize the larger effective nonlinear coefficient, the phase matching is based on type Ⅱ(B) (o→o+e). When the pump energy of the 1 064 nm laser is 89 mJ with a pulse width of 10 ns, an output energy of 7.5 mJ with a pulse width of 8.5 ns at 2.67 μm is obtained.