Provided are an underwater detector and a method for an underwater detection, and more particularly, an underwater detector including two direct current electrodes and a plurality of measurement electrodes in order to sense a movement of an object having conductivity different from that of water underwater. Since the underwater detector according to the present invention includes two direct current electrodes, a plurality of measurement electrodes, and a control and measurement module for measuring voltages of the plurality of measurement electrodes, the plurality of measurement electrodes each include an electrode control module and the electrode control module includes a first switch, a second switch, a controlling unit, and the like, the number of voltage measurement lines may be small and a voltage between two selected electrodes may be easily calculated.