For suppressing pedestal and cross-correlation noises in receiver, optical thresholder plays an important role in multiple-user optical code-division multiple access (OCDMA) system. Nonlinear optical loop mirror (NOLM) is an effective method to implement optical thresholder. The threshold characteristic is experimentally demonstrated and analyzed. The method of analyzing threshold by changing duty cycle of pump light is proposed, and the power at threshold point is 3.75 W for the pump duty cycle of 1/25. The relationship between output signal and wavelength spacing between signal and pump is discussed, and the optimal wavelength spacing is 5.8 nm at the threshold point. Experimental results show that when the duty cycle D=1/25, the pulse can be suppressed by 114.47 ps. The noise suppression result is given through eye diagram analysis of a receiver thresholder system built for the experiments.