Power　ultrasonic　systems　are　facing　challenge　in　amplitude　control　and　electro-mechanical　energy　conversion　efficiency　due　to　their　high　power　and　low　bandwidth.　In　this　paper,　a　novel　design　method　of　LC　matching　parameters　based　on　maximum　current　is　proposed　to　achieve　the　high-power　capacity　and　stable　vibration　of　the　ultrasonic　transducers.　The　electrical　model　of　the　ultrasonic　transducer　under　loading　conditions　is　constructed　by　the　joint　surface　dynamics　model.　The　relationship　between　the　equivalent　parameters　and　the　loading　pressure,　and　the　relationship　between　the　dynamic　branch　current　and　the　output　amplitude　are　obtained.　The　mathematical　model　of　ultrasonic　transducer　is　established.　A　composite　amplitude　control　algorithm　based　on　frequency　tracking　and　current　control　is　proposed.　The　frequency　tracking　algorithm　consists　of　fast　frequency　tracking　and　dynamic　branch　phase　locking.　The　fast　frequency　tracking　can　quickly　estimate　the　series　resonant　frequency　at　the　beginning,　and　the　dynamic　branch　phase　locking　continuously　tracks　the　series　resonant　frequency.　A　constant　current　control　algorithm　composed　of　expert　PI　(Proportional　Integral)　and　fuzzy　PI　is　designed.　According　to　the　voltage,　current　and　phase　difference　between　the　two　ends　of　the　ultrasonic　transducer,　the　PI　increment　is　calculated　to　adjust　the　duty　cycle　of　the　phase-shifted　full-bridge　to　track　the　target　current.　The　target　current　is　calculated　by　the　target　amplitude,　feedback　data　and　the　loading.　The　impedance　matching　experiment　is　carried　out,　and　the　output　current　can　reach　2A　under　the　impedance　matching,　and　the　amplitude　of　the　transducer　can　reach　80　mu　m.　The　experiments　under　variable　loads　are　carried　out　to　attain　the　equivalence　of　the　circuit　parameters　with　the　pressure　and　the　dynamic　branch　current.　The　experiment　of　amplitude　control　is　carried　out,　and　the　result　of　frequency　tracking　is　19680　Hz,　and　the　absolute　error　with　the　series　resonant　frequency　is　1　Hz.　The　absolute　error　between　the　output　amplitude　and　the　target　amplitude　can　be　controlled　within　1um,　and　the　relative　error　is　lower　than　6.7　%.