Marine　electromagnetic　transmitter　transmits　large　power　frequency　conversion　electromagnetic　wave　to　the　seabed　to　obtain　the　submarine　structure　and　mineral　resources,　however,　the　current　transmitter　has　the　problem　of　low　efficiency,　serious　heat　and　poor　ability　to　adapt　to　the　load,　for　which　the　use　of　soft-switching　circuit　controlled　source　is　to　reduce　circuit　losses.　The　mathematical　model　of　controlled　source　circuit　needs　to　be　established　to　realize　closed　loop　control　for　increasing　output　transient　performance　of　the　electromagnetic　wave.　Because　the　soft-switch　controlled　source　circuit　has　more　status　and　it　is　more　difficult　to　directly　model,　on　the　basis　of　modeling　of　hard　switching　controllable　source　circuit,　by　analyzing　the　impact　of　output　filter　inductor　current　transformer　leakage　inductance,　input　voltage　soft　switching　controllable　source　on　change　in　the　duty　cycle,　small-signal　model　of　soft-switching　circuit　is　established.　Finally,　simulations　and　experiments　verify　the　correctness　and　validity　of　the　model.　©　2016,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.