Abstract: Marine ecological environment monitoring urgently requires flexible flow sensing devices and systems. By natural selection, creatures have evolved a variety of highly sensitive organs for flow field perception, which provides a new biomimetic approach for researchers to develop flexible flow sensors. This paper reviews various flow-sensitive organs of aquatic animals, such as fish lateral line, harbour seal whiskers and crocodile dome receptors, and introduces their sensing principles and functions. Then, we describe the recent progress in bio-inspired flexible sensors for hydrodynamic perception, such as bio-inspired flow velocity sensors, bio-inspired pressure sensors and bio-inspired vortex sensors. Their application in flow field analysis for unmanned underwater vehicles (UUVs) and in wearable sensing for aquatic animals are described as well. Finally, we discuss the technological challenges and future trends of bio-inspired flexible hydrodynamic sensors, and outlooks their practical applications in the intelligent flow-field analysis.