We demonstrated an all-fiber mode-locked laser system which generated high-energy wave-breaking-free pulses with low repetition rate. The system included a passively mode-locked fiber laser which acted as a master oscillator and an Yb-doped fiber amplifier. By increasing the cavity length of the laser, pulse energy could be significantly increased. According to different cavity length, wave-breaking-free pulse with 2.9 nJ-6.9 nJ pulse energy and 870 kHz-187 kHz repetition rate has been achieved from the master oscillator. Over 4 microJ pulse can be obtained after amplification.