We demonstrate a high power high beam quality diode-pumped 1 112-nm Nd:YAG master-oscillator poweramplifier (MOPA) laser system. To increase the extraction efficiency and output power, a four-pass amplifier scheme is employed. Finally, the injected laser output power is amplified from 26 to 64 W with beam quality factor M2=2.85. Furthermore, a theoretical model that takes the temporal overlap inversion number dynamics into account is employed to analyze the performance of the MOPA laser system, and a good agreement with the experimental data is obtained.