Fiber intrusion detection sensor based on wavelength division multiplexing (WDM) is proposed to simplify the architecture of the system. The system uses different wavelengths to distinguish the different interfering sub-systems. WDM technique is used to multiplex the different wavelength interfering sub-system by the same interfering unit. In the receiver of the system, the signal of different wavelength interfering sub-systems is divided by the demutliplexing. Thus, the independent signal of different interfering sub-systems is achieved.