The theoretical analysis and experimental research of the optical parametric amplifier (OPA) based on periodically poled MgO:LiNbO3 (PPMgO:CLN) are presented. The quasi-phase-mathed (QPM) wavelength-temperature tuning curves and the curves of average power of each light versus crystal length are simulated, and the influencing factors of optimum length are investigated. When the crystal with grating period of 31.3 μm is operated at 150 ℃ and the OPA stage is pumped by a Q-switched NdYAG laser with average power of 44 W, the input idle power of 4 W at 2.765 μm is amplified by 13.3 W, and the conversion efficiency is 21.14%.