This paper describes the availability of the scale-space filtering for the underwater acoustic signal processing, and also presents the transmissing method utilizing the fingerprint pattern keying and the recognizing method of the fingerprint converted from the scale-space filtered input signal. The fingerprint pattern keying suitable to the scale-space filtering has a great advantage to reduce inevitable distortions which occur in underwater transmission. The demodulation of the fingerprint pattern keying is done to find the key pattern of the fingerprint. The neural network technique is used for this demodulation process. From simulating results have shown that the fingerprint pattern keying can be effective for underwater data transmission using the acoustic signal.