Abstract: In this paper, utilizing avalanche transistors as switching devices, the methods of designing and optimizing Marx circuit were discussed in detail. Modular improvement was implemented to the Marx circuit and a novel stereo structure of synchronous four-module combining was designed. The theoretical relation of the combining ratio and the combined modules were derived. Using a +300 V DC power and combining four -2.6 kV Marx modules, Gaussian pulses were obtained on a 50 resistive load with -5.0 kV magnitude, 5.3 ns half peak width, 2.0 mJ single-pulse energy. It was realized to stably work under a repetitive frequency of 10 kHz and the time delay jitter was measured less than 100 ps. The four-module combining efficiency was calculated up to 96.2 %. If changing the DC bias voltage between 200 V and 300 V and varying the number of combined modules, the final output magnitude would be regulated from 1.6 kV to 5.0 kV.