In this thesis, we experimentally demonstrate a passive mode-locked Erbium-doped fiber laser with large net round trip anomalous dispersion and nonlinearity through about 400m cavity length. The laser can output optical pulse trains at the low repetition rate around 500kHz and with the high pulse energy larger than 120nJ directly from the laser output. By adjusting the polarization controllers (PCs) and the pump power level, high energy pulses with square profile and nanosecond pulse-width without pulse breaking can be observed. Finally, we study the characteristic parameters of our pulses for further compressing the pulse-width to attain the short pulse-width and high peak power.