The mechanism of femtosecond optical pulse generation in a self-starting Er~(3+)-doped fiber ring solitonlaser and experimental research results are discussed. Using the nonlinear polarization rotation effect of the fiber for sat-urable absorbers (and then self-amplitude modulation) which acts as the mode locking mechanism in an Er~(3+)-dopedfiber ring cavity laser, stable self-starting mode locking pulses have been generated. The shortest output pulse is 269 fs,with the central wavelength of 1.531 μm at the repetition rate of 21.37 MHz. The average output powers of the two terminators of the laser are 0.25 mW and 0.08 mW respectively. The threshold pump power which sustains the mode lock-ing is 15 mW. Under high pump power, the laser works in a high order harmonic mode locking state. The mode lockingpulse durations vs different cavity lengths are also studied. The mechanism of femtosecond optical pulse generation in a self-starting Er ~ (3 +) - doped fiber ring solitonlaser and experimental research results are discussed. Using the nonlinear polarization rotation effect of the fiber for saturable absorbers (and then self-amplitude modulation) which acts as the mode locking mechanism in an Er ~ (3 +) - doped self-starting mode locking pulse have been generated. The shortest output pulse is 269 fs with the central wavelength of 1.531 μm at the repetition rate of 21.37 MHz. The average output powers of the two terminators of the laser are 0.25 mW and 0.08 mW respectively. The threshold pump power which sustains the mode lock-ing is 15 mW. Under high pump power, the laser works in a high order harmonic mode locking state. The mode lockingpulse durations vs different cavity lengths are also studied.