Abstract: For EMP effects experiments, a miniature Marx generator based on avalanche transistors is developed. The characteristics of avalanche transistor are analyzed and the principles of the pulse generator are studied. The design method of trigger circuit and pulse circuit is discussed, and the choice of device parameters is presented. A monopole and a dual polarity of 10-stage small-sized pulse generator are designed, which can yield double-exponential pulses with a rise time of several ns and a peak voltage of 1.8 kV, and the experimental results show that the output pulses have the virtue of high stability and high repetition rate.