The pulse trigger technology has a great influence on the output pulse of the Marx generator, and improving the trigger is of great significance to the stability, reliability and extensive use of the Marx generator. The research goal of this paper is to design a pulse transformer trigger to provide a 4MVMarx generator with a pulse whose front edge is less than 30ns, half-width is greater than 200ns and amplitude is 50kV. The design of pulse transformer is determined by the influence of transformer stray parameters - leakage inductance and distributed capacitance on the output pulse. In order to improve the steepness of the front edge of the output trigger pulse, a sharpening circuit is connected to the output side of the pulse transformer. Finally, the model of the pulse trigger unit is built and simulated by EMTP/ATP software, and the trigger pulse that meets the design requirements can be obtained, which realizes the optimized design of the pulse trigger unit.