Abstract: Glass is a non-conducting, hard and brittle material. It has a wide range of applications in optics, biomedicine and microelectromechanical systems. Electrochemical Discharge Machining (ECDM) is an effective microfabrication technique for insulating hard and brittle materials. It enables effective microstructural processing of glass. In ECDM, the discharge phenomenon is generated by the breakdown of the gas film, the quality of which, as the main medium in the process, is an important factor in forming good surface microstructures. This study focuses on the characteristics of the gas film and its influence on the discharge energy distribution. The study uses a full factorial test method with three factors and three levels of power supply, duty cycle and frequency as the influencing factors and gas film thickness as the response for the experimental study to obtain the best combination of process parameters for the best gas film quality. In addition, experiments were carried out on two types of glass, quartz glass and K9 optical glass, for the processing of micro-holes. The results show that the optimum combination of process parameters results in a thinner gas film and the best conditions for obtaining micro-holes with a smaller diameter overcut, a larger depth-to-diameter ratio and a smaller roundness error.