Intense electron beams with pulse duration on the level of microseconds have been utilized in a number of areas, including the production of free electron laser, material surface modification, and high-energy-density physics research. The high-voltage pulse forming technology based on metal oxide varistors (MOVs) has been verified to be an effective way to produce quasi-square pulses in recent years. In this article, a high-energy-density Marx generator with output waveform modified by a flat-top compensation LC filtering branch and a low inductance MOV folding structure was designed and tested to generate microsecond pulses. Experimental results show that a quasi-square pulse with a voltage amplitude of more than 500 kV and a pulsewidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\mu \text{s}$ </tex-math></inline-formula> was obtained on a dummy load of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\Omega $ </tex-math></inline-formula> . Further experimental research was carried out using a magnetically insulated coaxial diode (MICD) electron beam diode, and as a result, a relativistic electron beam with an energy of 550 keV, a current of 8.3 kA, a rise time of less than 40 ns, and a flat-top of about 600 ns was produced. The Marx generator with a modified waveform has the advantages of simple design, compact construction, and high-quality flat-top, which is a good platform for the generation of intense microsecond electron beams.