A new multi-area perimeter sensing system based on optical fiber wavelength division multiplexing (WDM) technology is proposed and demonstrated. The traditional single channel system with broadband mirror is improved by introducing fiber Bragg grating (FBG) as the mirror, and the number of the monitoring areas is expanded by using the FBG with different reflecting wavelengths matching the demodulation channels of a WDM apparatus. The WDM and FBG technology employed in the system makes the measurement in each channel independent, simultaneous, no mutual-interfering between channels sharing the same interference device. The experimental results show that the proposed perimeter sensing system is able to detect and recognize the perturbation localization simultaneously in each area or channel. The response time of the system is less than 1 ms, and crosstalk between channels is less than -20 dB.