The long cavity "8" shaped erbium-doped fiber laser to produce a square wave harmonic mode-locked pulses were studied experimentally. This type has a smooth broadband pulse spectrum shown as a square wave pulse on the oscilloscope, but confirmed that the autocorrelation trace of pulse noise categories, namely noise-square wave pulse. Experiment by adjusting the laser cavity parameters, such as polarization controller and pump power, gets up to 5th order harmonic mode-locked noise-square wave pulse. Experimental results show that the noise-square-wave pulses generated in the fiber laser is not infinitely increasing the pulse energy, but under certain conditions will produce a pulse division, square wave pulse harmonic mode locking phenomenon.