A novel nanosecond-pulsed, frequency-doubled green laser at 532 nm is reported, whose fundamental light is a dissipative soliton resonance (DSR) square-shaped, nanosecond pulse, which is obtained by all-fiber ytterbium-doped laser with master-oscillator power-amplifier (MOPA) system. The ytterbium-doped fiber seed laser generates stable DSR, square-shaped, nanosecond pulse by using nonlinear polarization rotation (NPR) modelocked technology. The pulse width of the fiber laser can be stably turned from 3 ns to 40 ns by just changing the pump power. After one stage non polarization-maintained ytterbium-doped fiber and two stages polarizationmaintained ytterbium-doped fiber amplification, the final output power is 6.95 W, corresponding to a peak power of 4.4 kW. The output of the all-fiber MOPA is launched into a 20 mm-long LBO crystal and a maximum secondharmonic power of 2.1 W is obtained at a fundamental power of 6.95 W with the optical conversion efficiency of 30.2%.