The tube leakage in the large power station boiler is the main reason for unplanned outage of power units. So how to prevent and control the leakage accident has become an important part of ensuring the safe operation of power grid. Sound spectrum analysis is the most commonly used detection method. At the top of the boiler, the temperature is high, and sometimes the positive pressure produced inside the boiler will make ordinary audio sensors particularly easily damaged. This paper designs a system of high temperature resistance fiber optic audio sensor and acoustic resonator. It can determine the parameter of fiber optic audio sensor, and double the leakage noise signal through the design of acoustic resonators. According to the experimental test results and theory, this system can effectively test leakage signal inside the boiler tube, and provide a new idea for leakage detection.