The underwater laminated sound-stealth sandwich composite structure can serve as an alternative to traditional sound-absorbing coatings for specific parts of underwater targets. This paper investigates the sound absorption mechanism based on viscoelastic material loss in underwater laminated sound-stealth sandwich composite structures. Sound tube tests were conducted to analyze the effects of filler dissipation, layered design, and backing conditions on the sound absorption coefficient. The experimental results indicate that the selection of viscoelastic sound-absorbing materials should not only control the loss factor range but also ensure that the characteristic impedance of the material matches the water. The addition of fillers shifts the first resonant peak frequency to lower frequencies. Glass microspheres yield higher sound absorption peaks, lower peak frequencies, and broader sound absorption bandwidths compared to mica fillers. An increase in the amount of fillers with medium to low diameters results in lower sound absorption peaks, higher peak frequencies, and broader sound absorption bandwidths. When the layers of the layered dissipative core material have similar thicknesses, the sound absorption coefficient is relatively low.