High-repetition-rate fiber laser has widely applications in the field of femtosecond frequency comb, ultra-fast optical sampling, and so on. In this paper, an Er-doped femtosecond fiber laser with a repetition rate of 303 MHz is demonstrated based on the mechanism of nonlinear polarization rotation. By means of optimization of cavity dispersion, the net dispersion in fiber cavity is a little negative nearby zero point. After mode locking, the laser is operating in the stretched-pulse regime. At a pump power of 817 mW, the output power of the laser is 125 mW in continue-wave state, and 69 mW in mode-locking state. The laser directly generates 90 fs before dispersion compensation. Mode locking can self-start at the pump power of 700-817 mW. Repetition rate drift of the mode-locked laser is 30 Hz in five hours.