Abstract: An ultra-sensitive distributed acoustic sensing (uDAS^®) seismograph is designed based on a high-performance phase-sensitive optical time domain reflectometer.Multi-frequency and random fiber laser amplification technologies combined with the interference demodulation method are adopted to achieve an accurate demodulation of the phase of the Rayleigh scattered light signal, which can be used for high-precision pickup of external sound waves/vibration signals.Experimental results show that uDAS^® has a noise floor of 4.5pε/ \sqrt \rmHz in the range of 1~500Hz.Moreover, it has the characteristics of linear amplitude response and long sensing distance.Compared with those obtained via electronic detectors, the recorded waveforms are highly consistent.uDAS^® has initially been used in borehole seismic monitoring, micro-logging, and other exploration activities, and has led to high quality production data.Currently, uDAS^® has great application prospects in petroleum exploration, such as in long-term dynamic monitoring and pipeline monitoring.