Characteristics of non-balanced Mach-Zehnder Interferometer (MZI) is analyzed.DWDM multiplexer/demultiplexer based on cascaded MZI is proposed and discussed.The simulation results show its spectrum performance,bandwidth of channel and isolation,and fiber grating could be used to enhance its isolation.This DEMUX can be used in at least 16 channels or 32 channels DWDM system.