Marine　electromagnetic　transmitter　transmits　electromagnetic　waves　with　large　power　frequency　conversion　to　the　seabed　to　obtain　the　submarine　structure　and　mineral　resources.　However,　the　current　transmitter　presents　several　problems,　such　as　low　efficiency,　serious　heat,　and　poor　adaptability　to　the　load.　Soft-switching　controlled-source　circuit　is　used　to　reduce　circuit　losses.　The　mathematical　model　of　controlled-source　circuit　should　be　established　to　realize　a　closed-loop　control　for　increasing　the　output　transient　performance　of　electromagnetic　waves.　Given　that　the　soft-switching　controlled-source　circuit　has　more　status　and　that　direct　modeling　is　difficult,　small-signal　model　of　soft-switching　controlled-source　circuit　is　established　based　on　that　of　hard-switching　controlled-source　circuit　by　analyzing　the　effect　of　output　filter　inductor　current　transformer　leakage　inductance　and　input　voltage　soft-switching　controlled　circuit　on　change　in　the　duty　cycle.　Finally,　experiments　verify　the　accuracy　and　validity　of　the　model.