The erbium-doped fiber oscillators, especially mode-locked fiber oscillators for generating femtosecond pulses, cannot meet the requirements for most of modern industrial applications because they are resticted by the low power and the limited wavelength range. In order to solve this problem, lots of efforts have been made both theoretically and experimentally, to improve the chirped pulse amplification (CPA) technology. The emergence of CPA technology greatly enhances the energy of laser pulses. The broadening and compressing of the laser pulses are both always dependent on the improving of spatial optical components, such as grating pairs. However, the use of this kind of method can increase the complexity of the amplification system to a certain extent. This may be an essential reason why more and more researchers pay attention to all fiber amplification system. In this paper, the master oscillator pulse nonlinear amplifier system based on all polarization- maintaining fiber is proposed, which is mainly composed of an oscillator based on the semiconductor saturable absorption mirror and linear cavity, a two-stage amplification and a pulse compressor constructed by a single-mode conductive fiber with anomalous dispersion. Using this system, we obtain ultrashort laser pulses in the 1.5 nm band whose pulse width equals 44 fs and single pulse energy reaches about 1 nJ. The system is not only compact and miniaturized but also stable and reliable due to the all polarization-maintaining fiber. Subsequently, an MgO doped periodically poled lithium niobite crystal with a thickness of 1 mm is used to implement frequency doubling. The pulses from the system are accurately focused on a position where the crystal polarization period is 19.8 μm with help of some wave plates and lenses. Adjusting the optical path reasonably and optimizing colliminated focusing parameters, the double-frequency pulse output with certral wavelength of 779 nm and average power of 60 W is obtained, in which the conversion efficiency reaches 30%. The result shows that the master oscillator pulse nonlinear amplifier system based on all polarization maintaining fiber can produce satisfactory ultrashort pulses. It is a new idea for generating the ultrashort femtosecond pulses in the near-infrared band.