Abstract: 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.