A master oscillator power amplifier (MOPA) structured pulsed fiber laser is reported. The single-frequency pulse seed, with the average power of 0.5 mW, is obtained by externally modulating a continuous wave laser with linewidth of 20 kHz. The pulse seed is firstly pre-amplified to about 2.7 W of average power with three Yb-doped fiber (YDF) amplifiers. The main amplifier is based on a large-mode-area (LMA) double clad YDF with core diameter of 30 μm and cladding diameter of 250 μm. When the pump power of the main amplifier is 87.1 W, a single-frequency pulsed laser with pulse duration of 10 ns and peak power of 486.7 W is generated. The average output power is 58.4 W.