We report on a nanosecond master oscillator /power amplifier architecture for optical parametric conversion of high pulse energy from 1.064μm to 1.572 μm in KTiOAsO4 crystal. The signal emission is amplified by two different parametric amplifier architectures respectively. By comparing the results obtained, a novel amplifier architecture is chosen which is expected to combine the high gain and good beam quality. With a seeding signal energy of 1 mJ, and 400mJ pump pulse at 100Hz, a gain up to 64 at 1.57μm with the beam quality M<sup>2</sup> less than 4.8 is realized. The total optical-optical conversion efficiency reached 16%.