The　objective　of　this　work　is　to　detect　underwater　sound　with　light　diffracted　by　liquid　surface　wave　(LSW).　An　experimental　setup　for　underwater　detection　with　a　converter　is　established.　The　diffraction　patterns　by　LSW　are　obtained.　By　analyzing　the　fringes,　the　characteristics　of　those　relating　to　both　amplitude　and　wavelength　of　LSW　and　underwater　sound　are　achieved.　Meanwhile,　the　transformation　model　of　waves　from　underwater　into　LSW　is　proposed.　The　dependence　of　the　amplitudes　on　the　diameter　of　the　converter　is　obtained　by　utilizing　droplet-floating　model.　Finally,　a　comparison　between　the　model　and　the　experiment　supports　these　observations.