A picosecond pulse laser with central wavelength of 1060 nm and adjustable output waveform is used as the seed source. This seed source is amplified by an Yb-doped double cladding fiber amplifier, and the output pulse width can be adjusted between 0.5~10 ns. In each waveform of the master oscillator power amplifier (MOPA) fiber laser, the highest average power is in the range of 18~21 W, peak power is in the range of 11~13 kW, and single pulse energy is in the range of 0.02~0.13 mJ with a near single-mode beam (M2=1.5). This high peak power, high single pulse energy and high average power fiber laser can meet the requirements of the area of the laser machining, material processing and the nonlinear transfer, and is a significant light source for some material which is sensitive to the heat when processed by lasers.