The invention discloses an underwater multi-channel data acquisition device. The device comprises a watertight installation bin; the watertight installation bin is equipped with a depth and temperature probe, a data communication connector, an analog signal input connector group, a power supply control switch jack and a power supply connector; the depth and temperature probe is used for acquiringunderwater working depth and temperature in real time when the underwater multi-channel data acquisition device is working; a data acquisition card is installed in the installation bin; the data acquisition card includes an analog-to-digital conversion module, a sampling control module and a power supply conversion module; and the analog-to-digital conversion module is watertightly connected withthe analog signal input connector group and is used for receiving analog voltage signals transmitted by the analog signal input connector group and converting the analog voltage signals into digital signals so as to realize multi-channel analog-to-digital conversion. The underwater multi-channel data acquisition device has the advantages of high applicability, high portability, low power consumption and the like. The invention can optionally provide a multi-channel data acquisition method.