A compact, coaxial configuration and fast-rising time Marx generator is designed, which uses a 3.3 nF ceramic capacitor as energy storage capacitor, a spiral-shaped air core inductor as a charging inductor, and generates voltage pulses by a quick gas discharge on the loads. The Marx is fitted into a tube with 14.5 cm diameter and a total length of 47.7 cm. The capacitors, charging inductors and spark gas switches are insulated with mixed gas of Sulfur hexafluoride(SF6) and Nitrogen(N2). By theoretical and circuit simulation, the influences of switch conduction states, distributed capacitance, loop inductance and stray capacitance on the output waveforms are discussed. The voltage output waveform on the load(50 Ω)of Marx generator is analyzed using the PSPICE, which shows that the output voltage is 150 kV, the open circuit voltage is up to 240 kV, the pulse width of load output waveform is about 25 ns with 10 ns rise-time, and energy of pulsed power source is 7.9 J. A lumped circuit description of the Marx that well matches the experimental results is also given.