The invention relates to a novel ship monitoring 
magnetic field sensor based on the ultrasonic sensing and magnetic detection technology. The sensor comprises a 
silicon substrate, a 
metal electrode, an insulating layer, a piezoelectric film, and a cavity filled with low concentration magnetic fluid. The sensor is characterized in that the sensor can emit or receive an ultrasonic wave, the 
viscosity of the magnetic fluid in the cavity is very sensitive to an external 
magnetic field, in the condition of no magnetic abnormal source, the sensor carries out 
ultrasonic detection in a mode of an 
underwater acoustic 
transducer, when a magnetic abnormal source appears, the sensor can carry out 
ultrasonic detection and magnetic detection at the same time, and the ultrasonic frequency emitted by the sensor can be controlled by applying a bias 
magnetic field. The ship monitoring magnetic field sensor is manufactured by using the advanced 
micro nano processing technology, the volume is small, the 
power consumption is low, the 
frequency band is wide, a one-dimensional 
line array (1D) and a two-dimensional surface array (2D) can be made, the sensor is compatible with a front-end 
electronic circuit, the 
mass production of devices is facilitated, and the sensor is suitable for coastal defense, anti 
submarine, warship detection, ocean 
topography detection and the like.