In a two-stage optical parametric amplifier based on KTiOAO4 crystals, we apply beam-overlapping technique to nanosecond signal pulse amplification, which results in high conversion efficiency and good beam quality. A signal pulse energy of 66 mJ at 1.572 μm wavelength is generated with 220 mJ of pump pulse input. A maxi-mum gain of 66 and a maximum pump depletion of as high as 44% are determined. The spectral linewidth of the amplified signal pulse is around 50 MHz, and the beam quality factor of M.2 is less than 2.3.