The invention discloses a steel plate full covering supersonic wave detection device, and a method. The steel plate full covering supersonic wave detection device comprises a mechanism capable of walking on a steel plate freely, a multichannel supersonic wave flaw detector, a plurality of probes which are connected with the multichannel supersonic wave flaw detector in corresponding connection andare arranged in linear arrays, a laser movable inductor, a coupling device, a host computer, and a power source; the axis of the probes is vertical to a steel plate plane to be detected; the multichannel supersonic wave flaw detector is used for controlling the probes to send / receive supersonic wave signals, performing analog-to-digital conversion, and sending signals to the host computer; the laser movable inductor is connected with the plurality of probes in linear arrays and the host computer respectively; the host computer is used for obtained real-time two-dimensional position signals from the laser movable inductor for subsequent defect signal analysis, processing, and positioning; the coupling device is used for supplying the probes in linear arrays with a couplant; the power supply is used for providing the multichannel supersonic wave flaw detector, the host computer, and the laser movable inductor with electricity. The advantages are that: detection transverse resolution isincreased, and rapid, accurate, and comprehensive detection of steel plate internal defects is realized based on the limit number of the probes of a conventional portable steel plate detection vehicle.