A pulsed fiber laser based on master-oscillator power amplifier(MOPA) architecture is reported. In order to get a high repetition rate, high peak power,and high beam quality laser, a laser diode(LD) pumped acoustic-optic Q-switched Nd∶GdVO4 solid-state laser is used as a seed source. The seed laser with output power of 2 W is amplified by Yb-doped double-cladding fibers in two stages whose core diameters are 20 μm and 80 μm. At repetition rate of 50 kHz, average output power of 103 W is generated. The highest peak power is up to 162 kW, pulse duration is 12.7 ns,and M2 value is 4.3.