The HTD-42 low-noise hydrophone is a streamlined cylindrical structure device designed specifically for deep-sea acoustic monitoring. Its self-noise level is lower than the zero level sea state background noise, and it can be adapted to two piezoelectric ceramic units with different pressure depths. It has an ultra wideband horizontal omnidirectional response of 10Hz-80kHz and currently supports preamplifiers up to 60dB. The hydrophone is capable of long-term stable operation in the depths of 4500 meters or 6800 meters underwater. Its fluid dynamics optimization design significantly reduces resistance and turbulent noise, making it suitable for high-sensitivity acoustic signal acquisition scenarios such as marine biological observation, seabed exploration, underwater communication, and ship noise monitoring.