Here,　based　on　the　equivalent　zero　mass　feature　of　acoustic　superstructure,　a　radiation　cover　plate　what　is　the　core　component　of　a　superstructure　underwater　acoustic　projector　was　designed　to　reveal　the　local　resonance　acoustic　radiation　mechanism　and　multi-element　synergistic　coupling　acoustic　radiation　mechanism.　The　equivalent　zero　mass　design　made　the　structure　produce　local　resonance,　obtain　large　surface　vibration　velocity,　and　achieve　higher　radiation　sound　pressure　level.　Meanwhile,　the　synergistic　coupling　among　multi-element　was　used　to　realize　structure＇s　local　resonance　at　different　positions　and　great　expansion　of　working　frequency　band.　Based　on　this　mechanism,　a　new　type　small-size,　low-frequency　and　large　broadband　superstructure　underwater　acoustic　projector　was　designed.　Its　structural　parameters　were　optimized　with　the　finite　element　method.　According　to　the　optimization　results,　a　test　prototype　was　made　with　diameter　of　400　mm,　height　of　240　mm　and　total　weight　of　46　kg.　The　test　results　showed　that　the　projector　has　a　better　emission　response　within　the　range　of　40-1　050　Hz,　and　the　average　emission　current　response　is　about　146　dB,　they　are　basically　consistent　to　the　theoretical　simulation　results;　the　study　content　here　can　provide　a　new　idea　for　development　and　improvement　of　underwater　acoustic　projector　structure,　and　has　a　certain　application　prospect.　©　2022,　Editorial　Office　of　Journal　of　Vibration　and　Shock.　All　right　reserved.