The pulse source technology that can generate high repetition frequency pulse signals is being used in more and more fields, such as electromagnetic interference, biomedicine, precision instrument control, radar detection, etc. Developing pulse signals with high repetition frequency and narrow pulse width parameters is a challenging aspect of this technology. However, in this paper, using avalanche transistors as fast-switching devices helps to address this challenge. The authors have developed a pulse source based on the Marx circuit by optimizing various parameters of the circuit components, improving the circuit layout, and designing impedance matching. This pulse source can generate a negative pulse signal with specific characteristics of a falling edge of 140 ps, an amplitude of 620 V, and a half-peak pulse width of 170 ps when operating under a matched load of 50 Ω. To ensure stable operation and prolonged circuit life, a combination of water cooling and a semiconductor heat sink is utilized for heat dissipation. This allows the pulse source to work reliably at a repetition frequency of 300 kHz for more than 30 minutes.