MILO development has garnered increased attention due to its ability to generate high power microwaves without relying on an external magnetic field. Instead, it utilizes self-generated magnetic fields. The oscillator’s anode which is part of slow wave structures, composed of thin conductive vanes creating cavities between them. The anode and cathode are separated by a gap, where cross field magnetic fields serve to insulate and confine the electron flow. This paper presents modelling and simulations carried out using CST software, exploring the effects of voltage and electrode gap in S-band MILO structure. The proposed design is simulated for maximum output power of 2.3 GW with beam voltage of −600 kV, and beam current of 45 kA, with specified gap of 14 mm in S Band frequency. And also, the simulation was carried out for the variation in voltage from −200 kV to −600 kV and electrode switch gap parametric from 5 mm to 15 mm.