The main frame of the distributed fiber optic leak detection system adopted the hybrid Mach-Zehnder & Sagnac interferomtric. We use the sensing fiber of In-Line frame to detect leak physical field. We can measure the position of the leak physical field through our sensing system and signal process system. In the cause of improving detective ability of leak detection system, we modify three elements of the system, including (1) the choice of the acoustic response of sensing fiber, (2) modification of the PZT phase modulator, and (3) modification of the PGC demodulator. The frame of our experiment is composed of the distributed fiber optic leak detection system and leak system of the fluid pipes. In which leak system of fluid pipes is designed the leaky frame of high-pressure fluid pipes. The main of experiment introduce the leak detection system to measure the leak acoustics of the fluid pipes. Then we can discuss the experimental result. The measurable minimum range of our distributed fiber optic leak detection system is3.3x10^-4(rad/¡ÔHz), and the dynamic range is above 75 dB. The dynamic range of this system can improve the original system to above 15 dB.