A distributed fiber optic intrusion sensor system based on Brillouin optical time-domain reflectometer(BOTDR) has been presented.With the application of a single longitudinal mode distributed feedback(DFB) laser and the sideband-pass filter(BPF) technique,the frequency demodulation of the system can be simplified,and the fast detection of the intrusion events can be achieved.The results show that the spatial resolution can reach 5 m with a strain resolution of 200 με in the measuring range of 10 km for this system,which can meet the requirements of the real-time intrusion detection.