A pulse master oscillator power amplifier (MOPA) system, which can provide high repetition rate and nanosecond pulse laser, was constructed by China-made large-mode-area(LMA) fiber and single mode 1064 nm laser-diode(LD) with fiber cascaded amplification system used as seed laser. The system generates up to 59 W average power of amplified radiation at a wavelength of 1064 nm with pulse duration of 22.7 ns(at 50 kHz repetition rate) and adjustable repetition frequency of 50～150 kHz. Some basic characteristics of this system, including the pulse temporal characteristics as well as the emission spectrum characteristics are investigated experimentally, and the impacts of the power amplification of the fiber to the pulse duration are analyzed.