Abstract: Ground electromagnetic detection system（SEP） transmitter is developed on the basis of the principle of high-power switching power,. As the key part of SEP transmitter transformer’s quality relates to the overall working condition of transmitter. Considering the special requirements of 20 KHZ transmitter high-voltage power and bear ability of power semiconductor devices,designing a 20 KHZ double input two output power transformer and using the finite element analysis of ANSYS Maxwell carried out 3D modeling of transformer,analyzing its internal distribution of the electromagnetic field. At the same time Transformer have been designed to put into transmitter system in using,and applied in the relevant field experiment. The simulation and experiment indicated that this transformer is designed reasonable,it has small ripple,low loss,low temperature,high efficiency,stability and reliability.