In order to realize the high repetition rate operation in Q-switching with good beam quality. A diode-pumped acousto-optic(AO) Q-switched master oscillator power amplifier (MOPA) all-solid-state laser with high repetition rate and high power was demonstrated by using a master oscillator power amplifier with two-pass amplification configuration. The structure and relevant parameters of the master oscillator power amplifier(MOPA) were optimized, the research of the high power MOPA system was completed. Through arranging the optical components in the resonator reasonably to improve beam quality, the focusing lens and aperture were used to achieve the laser mode matching. The maximum average power of the MOPA system is 51.3 W. Short pulses of 18.62 ns with beam quality M■■=1.882, M■■=1.971 at 50 kHz. And the corresponding total optical-to-optical efficiency is 23.75%. With the help of gain guiding effect, the quality of the beam which emitted from master oscillator power amplifier(MOPA) laser system can be improved.