In view of the problem that the testing optical path of the Brillouin optical time domain analyzer(BOTDA) is prone to failure in long-term use, which leads to the interruption of BOTDA testing, an optical path automatic switching protection system based on the principle of optical time domain reflectometer(OTDR) is designed. The system takes K60 controller as the control core, uses the FLEXBUS interface to mount SRAM, FPGA and W5300, integrates the OTDR module of K60+FPGA architecture, realizes the optical path switching through the optical switch, monitors the failure of each optical path, and can switch the optical path and send the short message alarm when the optical path fails in the BOTDA test; introduces the system principle, main hardware modules, ethernet guidance and upgrading and optical path self dynamic switch protection software process. The experimental results show that the OTDR dynamic range is more than 35 dB, which meets the monitoring requirements of BOTDA test optical path.