In this paper, a single-pulse discharge experimental device has been developed to study the mechanism of high speed small hole EDM drilling. It is found that the emulsion used in high speed small hole EDM drilling as dielectric fluid is easier to be broken down than the kerosene which is always used in the traditional EDM. The injection flushing is contributive to the ejection of molten material in the crater produced by discharge, and can greatly improve the evacuating condition. Additionally, the effective quenching ability of emulsion and injection flushing can greatly reduce the necessary pulse interval and increase the effective pulse frequency.