The switching characteristics of a NOLM demultiplexer are investigated by using an analytic and numerical methods. The results reveal that the switching characteristics of a NOLM demultiplexer depend on parameters such as the power coupling ratio of the coupler,the peak power of control pulses,the walk-off and the initial time delay between signal pulses and control pulses,etc. The efficiency of NOLM is dependent on the peak power of control pulses. However,the switching window profile begins to oscillate as the power exceeds a critical value and this will be detrimental to the demultiplexed signals. The signal-control pulse walk-off can broaden the switching window of NOLM,make the window profile deviate from its central position,and decrease its switching efficiency.