Abstract: A compact 200 kV pulse transformer with step-up ratio of 109 was developed to miniaturize high-voltage pulse transformer. Researches on coupling, high-voltage insulation and output characteristics of the transformer were carried out by electromagnetic theory, circuit simulation and experiments. Important parameters were calculated and designed. As the closed magnetic core of the transformer was made of crystal-tropism siliconsteel strip, the effective coupling coefficient reached as high as 0.95. With insulated structure of polymeric cylinder and alternate-winding method, the secondary windings of transformer could deliver a high-voltage pulse of 230 kV and full width at half maximum (FWHM) of 3 μs when initial voltage of the primary energy-storage capacitor was 2.1 kV. Results of simul