Aiming at the requirements of low power consumption, miniaturization, and massive data processing, a modular distributed optical fibre acoustic sensing (DAS) demodulation system based on ultra-weak fibre Bragg grating (UW-FBG) is proposed. A highly integrated circuit and embedded system is used for the time-domain positioning and data acquisition of the gratings. Field programmable gate array (FPGA) demodulates the phase changes of each sensing section in real time. The demodulation outputs are uploaded through a Gigabit Ethernet connection. Through innovative software and hardware design, the demodulation system power consumption is less than 20 W, and the device volume is 250 mm× 180 mm× 45 mm, and the output data size is about 2.6% of the conventional methods. All the outputs are then tested on a piezoelectric transducer (PZT) platform. Results show that the background noise within 5 Hz–1280 Hz range is 2.16 pε/√(Hz), and the strain sensitivity reaches 484 pε/√(Hz)@200 Hz. The correlation coefficient of voltage and phase is 0.9991, which shows good linearity. Combined with a common commercial laptop to demodulate the micro-vibration signals, this system could provide a cost-effective scheme for acquiring acoustic-level micro-vibration signals and on-line field monitoring.