High average power linearly-polorized picosecond pulsed laser sources have a wide range of applications in the fields of industrial material processing, coherent beam combination and nonlinear optics. A high power linearly polarized picosecond pulse ytterbium-doped all-fiber laser based on a seed of mode-locked fiber laser with a semiconductor saturable absorber mirror is reported. The fiber laser is constructed with a two-stage master oscillator power amplifier (MOPA) configuration. Stable mode-locked pulse train occurs when the incident pump power increasing and the pulse repetition rate is 40 MHz in a ring cavity configuration. Increasing the incident pump power to 200 mW, the maximum output average power is 12 mW. The pulse width is measured to be 20 ps. The center wavelength and the spectrum bandwidth are 1038.2 nm and 1.7 nm, respectively. The steep edge in the optical spectrum is a clear indication of the dissipative solitons (DSs) in this all-normal-dispersion mode-locked fiber laser. After two-stage fiber amplifier with the polarization maintaining double-cladding ytterbium-doped fiber as the gain medium, 5 W average output power is achieved, corresponding to a single pulse energy of 125 nJ and a peak power of 6.25 kW, respectively. No undesirable nonlinear processes such as stimulated Raman scattering are observed. At this high output power, the spectrum bandwidth and the pulse width are measured to be 3.1 nm and 20 ps, respectively, and the polarization extinction ratio is 20 dB.