The erosion feature of single electrical discharge pulse is the base unit of electrical discharge machining. Research on the erosion feature of single electrical discharge pulse is of great significance on understanding the process of electrical discharge machining and choosing the electrical parameter. Firstly, the material erosionmechanism of single electrical pulse was introduceed.Secondly, a simulation about the thermalconductivity process of energy within the material was carried out based on the electricitythermo model by using ANSYS, an regular that molten zone radius of the material varies with the pulse width was obtained. Finally, a series of experiments including different pulse width and polarity were carried out in the microEDM machine tool which had been developed by Institute of machinery manufacturing technology. The experimental results indicate that no mater what the polarity is,the diameter, depth and erosionvolume of electrical pit will increase while the diameterdepth ratio will decrease with the pulse width increasing; the diameter, depth and erosionvolume of electrical pit are greater when workpiece is used as cathode,while the diameterdepth ratio is smaller in the same pulse width; polarity erosionratio of electrical pit will decrease with the pulse width increasing.