According to the nonlinear polarization rotated effect, a self-starting mode-locked ring cavity fiber laser is obtained and optimized through changing the fiber length and coupler parameters. As the seed of an all-fiber ultra-short pulse amplifier with master oscillator power amplifier (MOPA) structure, the pulse which has 2.042 W in average power, 1 063.8 nm in wavelength, 41.3 MHz in repetition frequency, 45 ps in impulse duration, 49.4 nJ in single pulse power and 1.1 kW in peak power, is realized, taking double-cladding fiber as the gain medium. The optical conversion efficiency of the whole system is 40.8%, which could be supportable to the higher power all-fiber pulse laser.